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CRISBERT I. CUALTEROS, M.D.
(+63919)8586556
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Content of the new page
World Health Organization
WHO
Background document:
The diagnosis, treatment and
prevention of typhoid fever
WHO/V&B/03.07
ORIGINAL: ENGLISH
Communicable Disease Surveillance and Response
Vaccines and Biologicals
WHO/V&B/03.07
ORIGINAL: ENGLISH
WHO
Background document:
The diagnosis, treatment and
prevention of typhoid fever
World Health Organization
Communicable Disease Surveillance and Response
Vaccines and Biologicals
The Department of Vaccines and Biologicals
thanks the donors whose unspecified financial support
has made the production of this publication possible.
This document contains general background information on the epidemiology, infection,
diagnosis, treatment and prevention of typhoid fever. It is targeted at public health
professionals, clinicians and laboratory specialists. A second document to be published
later, targeting health professionals in the field, will focus on the practical aspects of
epidemic preparedness and the treatment of the disease.
-
-
Ordering code: WHO/V&B/03.07
Printed: May 2003
This publication is available on the Internet at:
www.who.int/vaccines-documents/
Copies may be requested from:
World Health Organization
Department of Vaccines and Biologicals
CH-1211 Geneva 27, Switzerland
• Fax:
+ 41 22 791 4227 • Email: vaccines@who.int •
© World Health Organization 2003
All rights reserved. Publications of the World Health Organization can be obtained from Marketing
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The designations employed and the presentation of the material in this publication do not imply the
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The mention of specific companies or of certain manufacturers’ products does not imply that they are
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The World Health Organization does not warrant that the information contained in this publication is
complete and correct and shall not be liable for any damages incurred as a result of its use.
Contents
Abbreviations .................................................................................................................... v
Acknowledgements ........................................................................................................ vii
Chapter 1: The organism, the disease and transmission ....................................... 1
1.1 The organism ....................................................................................................... 1
1.2 The disease ........................................................................................................... 1
1.3 Contamination and transmission ....................................................................... 4
Chapter 2: Diagnosis of typhoid fever ....................................................................... 7
2.1 Specimens ............................................................................................................. 7
2.2 Microbiological procedures ............................................................................... 9
2.3 Serological procedures ...................................................................................... 11
2.4 Antimicrobial susceptibility test for typhoid fever organisms .................... 16
2.5 Storage of typhoid fever organisms ................................................................ 17
2.6 Quality control .................................................................................................. 17
Chapter 3: Treatment of typhoid fever ................................................................... 19
3.1 General management ........................................................................................ 19
3.2 Antimicrobial therapy ....................................................................................... 19
3.3 Management of complications ......................................................................... 22
3.4 Management of carriers .................................................................................... 23
Chapter 4: Prevention of typhoid fever ................................................................... 25
4.1 Safe water ........................................................................................................... 25
4.2 Food safety ......................................................................................................... 25
4.3 Sanitation ............................................................................................................ 26
4.4 Health education ............................................................................................... 26
4.5 Vaccination ......................................................................................................... 26
Conclusions .................................................................................................................... 30
References ...................................................................................................................... 31
Ig immunoglobulin (IgG, IgM)
i.m. intramuscular
i.v. intravenous
LPS lipopolysaccharide
MDR multi-drug resistant
Mp macrophages
NARST nalidixic-acid-resistant
Salmonella typhi
Vi virulent (antigen)
Abbreviations
We would like to thank the following for their participation in the preparation of
this document:
Dr Camilo Acosta, International Vaccine Institute, Seoul, Republic of Korea
Dr M. John Albert, Faculty of Medicine, Kuwait University, Kuwait
Dr M.K. Bhan, All India Institute of Medical Sciences, New Delhi, India
Dr Zulfiqar Bhutta, Aga Khan University, Karachi, Pakistan
Dr Robert Breiman, International Centre for Diarrhoeal Diseases Research, Dhaka,
Bangladesh
Dr John Clemens, International Vaccine Institute, Seoul, Republic of Korea
Dr Jeremy Farrar, Oxford University and the Hospital for Tropical Diseases,
Ho Chi Minh City, Viet Nam
Dr Asma Ismail, Universiti Sains Malaysia, Kelantan, Malaysia
Dr Keith Klugman, Emory University, Atlanta, USA
Dr Claudio F. Lanata, Instituto de Investigación Nutricional, Lima, Peru
Dr Myron M. Levine, University of Maryland School of Medicine, Baltimore, USA
Dr Pakleong Lim, Clinical Immunology Unit, The Prince of Wales Hospital, Shatin,
Hong Kong, People’s Republic of China
Dr Maria Neira, Department of Communicable Disease Prevention, Control and
Eradication, World Health Organization, Geneva, Switzerland
Dr Henk L. Smits, KIT Biomedical Research, Royal Tropical Institute/Koninklijk
Instituut voor de Tropen, Amsterdam, Netherlands
Dr Tikki Pang, Department of Evidence and Information for Policy, World Health
Organization, Geneva, Switzerland
Dr Christopher Parry, Department of Medical Microbiology University of Liverpool,
United Kingdom
Acknowledgements
Dr Narain Punjabi, US NAMRU-2, Jakarta, Indonesia
Dr Philippe Sansonetti, Institut Pasteur, Paris, France
Dr Shosun Szu, NIH, Bethesda, USA
Dr John Wain, Imperial College Medical School, London, United Kingdom
under the coordination of
Dr Bernard Ivanoff, Department of Vaccines and Biologicals
and
Dr Claire Lise Chaignat, Department of Communicable Disease Surveillance
and Response
WHO/V&B/03.07 1
Chapter 1:
The organism, the disease
and transmission
1.1 The organism
Typhoid fever is caused by
but often less severe disease is caused by
The nomenclature for these bacteria is confused because the criteria for designating
bacteria as individual species are not clear. Two main views on the nomenclature of the
genus
should be recognized:
six subspecies, of which subspecies I (one) contained all the pathogens of warm-blooded
animals.
serotype
because the name was not well known to clinicians and its use might cause accidents
endangering health or life. The original rules therefore remain in force. Ezaki and
colleagues have noted in the International Journal of Systematic and Evolutionary
Microbiology that the correct nomenclature for the causal agent of typhoid fever is
Salmonella typhi, a Gram-negative bacterium. A very similarSalmonella serotype paratyphi A.Salmonella have been discussed. Le Minor and Popoff suggested that two speciesSalmonella bongori and Salmonella enterica. S. enterica includedS. typhi was a serotype within subspecies I: Salmonella enterica subspecies Ityphi. This proposal was rejected by the International Judicial Commission
Salmonella typhi
and have requested that the current subspecific status of serotype
paratyphi
A should be raised to specific status, i.e. Salmonella paratyphi A.
S. typhi
a result of early genetic studies and the recent sequencing of the whole genome.
Although many genes are shared with
there are several unique clusters of genes known as pathogenicity islands and many
more single genes that seem to have been acquired by
has several unique features, the genetic basis of many of which is known asE. coli and at least 90% with S. typhimurium,S. typhi during evolution.
S. typhi
(see Chapter 2). One of the most specific is that of polysaccharide capsule Vi, which is
present in about 90% of all freshly isolated
the bactericidal action of the serum of infected patients. This capsule provides the basis
for one of the commercially available vaccines (see Chapter 4). Vi antigen is present in
some other bacteria (
dublin
can be identified in the laboratory by several biochemical and serological testsS. typhi and has a protective effect againstCitrobacter freundii, Salmonella paratyphi C and Salmonella) but not in exactly the same genetic context. The ratio of disease caused by
S. typhi
this matter has been studied.
to that caused by S. paratyphi is about 10 to 1 in most of the countries where
1.2 The disease
During an acute infection,
being released into the bloodstream. After ingestion in food or water, typhoid organisms
pass through the pylorus and reach the small intestine. They rapidly penetrate the
mucosal epithelium via either microfold cells or enterocytes and arrive in the lamina
propria, where they rapidly elicit an influx of macrophages (Mp) that ingest the bacilli
but do not generally kill them. Some bacilli remain within Mp of the small intestinal
S. typhi multiplies in mononuclear phagocytic cells before
2 The diagnosis, treatment and prevention of typhoid fever
lymphoid tissue. Other typhoid bacilli are drained into mesenteric lymph nodes where
there is further multiplication and ingestion by Mp. It is believed that typhoid bacilli
reach the bloodstream principally by lymph drainage from mesenteric nodes,
after which they enter the thoracic duct and then the general circulation. As a result of
this silent primary bacteraemia the pathogen reaches an intracellular haven within
24 hours after ingestion throughout the organs of the reticuloendothelial system (spleen,
liver, bone marrow, etc.), where it resides during the incubation period, usually of 8 to
14 days. The incubation period in a particular individual depends on the quantity of
inoculum, i.e. it decreases as the quantity of inoculum increases, and on host factors.
Incubation periods ranging from 3 days to more than 60 days have been reported.
Clinical illness is accompanied by a fairly sustained but low level of secondary
bacteraemia (~1
10 bacteria per ml of blood).
1.2.1 Symptoms
The clinical presentation of typhoid fever varies from a mild illness with low-grade
fever, malaise, and slight dry cough to a severe clinical picture with abdominal discomfort
and multiple complications. Many factors influence the severity and overall clinical
outcome of the infection. They include the duration of illness before the initiation of
appropriate therapy, the choice of antimicrobial treatment, age, the previous exposure
or vaccination history, the virulence of the bacterial strain, the quantity of inoculum
ingested, host factors (e.g. HLA type, AIDS or other immunosuppression) and whether
the individual was taking other medications such as H2 blockers or antacids to diminish
gastric acid. Patients who are infected with HIV are at significantly increased risk of
clinical infection with
S. typhi and S. paratyphi (1). Evidence of Helicobacter pylori
infection also represents an increased risk of acquiring typhoid fever.
fever, disturbances of bowel function (constipation in adults, diarrhoea in children),
headache, malaise and anorexia. Bronchitic cough is common in the early stage of
the illness. During the period of fever, up to 25% of patients show exanthem (rose
spots), on the chest, abdomen and back.
Acute non-complicated disease: Acute typhoid fever is characterized by prolonged
setting and the quality of available medical care, up to 10% of typhoid patients
may develop serious complications. Since the gut-associated lymphoid tissue
exhibits prominent pathology, the presence of occult blood is a common finding
in the stool of 10-20% of patients, and up to 3% may have melena. Intestinal
perforation has also been reported in up to 3% of hospitalized cases. Abdominal
discomfort develops and increases. It is often restricted to the right lower quadrant
but may be diffuse. The symptoms and signs of intestinal perforation and peritonitis
sometimes follow, accompanied by a sudden rise in pulse rate, hypotension, marked
abdominal tenderness, rebound tenderness and guarding, and subsequent
abdominal rigidity. A rising white blood cell count with a left shift and free air on
abdominal radiographs are usually seen.
Altered mental status in typhoid patients has been associated with a high case-fatality
rate. Such patients generally have delirium or obtundation, rarely with coma. Typhoid
meningitis, encephalomyelitis, Guillain-Barré syndrome, cranial or peripheral neuritis,
and psychotic symptoms, although rare, have been reported. Other serious
complications documented with typhoid fever include haemorrhages (causing rapid
death in some patients), hepatitis, myocarditis, pneumonia, disseminated intravascular
Complicated disease: Acute typhoid fever may be severe. Depending on the clinical
WHO/V&B/03.07 3
coagulation, thrombocytopenia and haemolytic uraemic syndrome. In the pre-antibiotic
era, which had a different clinical picture, if patients did not die with peritonitis or
intestinal haemorrhage, 15% of typhoid fever cases died with prolonged persistent
fever and diseases for no clear reason. Patients may also experience genitourinary tract
manifestations or relapse, and/or a chronic carrier state may develop.
harbouring
Carrier state: 15% of patients, depending on age, become chronic carriersS.typhi in the gallbladder.
1.2.2 Magnitude of the problem
Typhoid fever is a global health problem. Its real impact is difficult to estimate because
the clinical picture is confused with those of many other febrile infections. Additionally,
the disease is underestimated because there are no bacteriology laboratories in most
areas of developing countries. These factors are believed to result in many cases going
undiagnosed. On the basis of the literature (2, 3) and the incidence of typhoid fever
recorded in control groups in large vaccine field trials with good laboratory support it
has been estimated that approximately 17 million cases of typhoid fever and 600 000
associated deaths occur annually (4). However, the estimates have been biased because
study populations have usually been in areas of high incidence. Furthermore, these
estimates of burden relate to the clinical syndrome of typhoid fever but not to
S. typhi
exposure. Since the prevalence of bacteraemia in febrile children is quite high (2
in areas of endemicity it is suggested that exposure to the bacteria is higher than indicated
by the figures that are based solely on the clinical syndrome of typhoid fever.
The incidence of the disease in areas of endemicity may resemble the incidences
observed in control groups in large vaccine field trials, viz. between 45 per 100 000
per year and over 1000 per 100 000 per year. Preliminary results from recent studies
conducted in Bangladesh by ICDDR,B show an incidence of approximately 2000 per
100 000 per year. Typhoid fever also has a very high social and economic impact because
of the hospitalization of patients with acute disease and the complications and loss of
income attributable to the duration of the clinical illness (5). It is important to note
that reports from some provinces in China and Pakistan have indicated more cases of
paratyphoid fever caused by
In areas of endemicity and in large outbreaks, most cases occur in persons aged between
3 and 19 years. In 1997, for example, this age range was reported during an epidemic of
the disease in Tajikistan. Nevertheless, clinically apparent bacteraemic
in children aged under three years has been described in Bangladesh, India, Jordan,
Nigeria, and elsewhere (6, 7). In Indonesia there is a mean of 900 000 cases per year
with over 20 000 deaths. In Indonesia, people aged 3
cases of typhoid fever and the attack rate of blood-culture-positive typhoid fever was
1026 per 100 000 per year. A similar situation was reported from Papua New Guinea.
When typhoid fever was highly endemic in certain countries in South America the
incidence of clinical typhoid fever in children aged under 3 years was low. In Chile,
however, single blood cultures for all children aged under 24 months who presented at
health centres with fever, regardless of other clinical symptoms, showed that 3.5% had
unrecognized bacteraemic infections caused by
Enteric fever had not been suspected on clinical grounds in any of the children.
In South America the peak incidence occurred in school students aged 5
in adults aged over 35 years. This kind of study has not been conducted in other areas
of endemicity.
3%)S. paratyphi A than by S. typhi.S. typhi infection19 years accounted for 91% ofS. typhi or S. paratyphi (8).19 years and
4 The diagnosis, treatment and prevention of typhoid fever
Between 1% and 5% of patients with acute typhoid infection have been reported to
become chronic carriers of the infection in the gall bladder, depending on age, sex and
treatment regimen. The propensity to become a carrier follows the epidemiology of
gall bladder disease, increasing with age and being greater in females than in males.
The propensity to become a chronic carrier may have changed with the present
availability and selection of antibiotics as well as with the antibiotic resistance of the
prevalent strains. The role of chronic carriers as a reservoir of infection was studied
in Santiago, Chile, where a crude rate of 694 carriers per 100 000 inhabitants was
found (9).
1.2.3 Case definition
Confirmed case of typhoid fever
A patient with fever (38°C and above) that has lasted for at least three days, with a
laboratory-confirmed positive culture (blood, bone marrow, bowel fluid) of
S. typhi.
Probable case of typhoid fever
A patient with fever (38°C and above) that has lasted for at least three days, with a
positive serodiagnosis or antigen detection test but without
S. typhi isolation.
Chronic carrier
Excretion of
cultures) for longer than one year after the onset of acute typhoid fever. Short-term
carriers also exist but their epidemiological role is not as important as that of chronic
carriers. Some patients excreting
S. typhi in stools or urine (or repeated positive bile or duodenal stringS. typhi have no history of typhoid fever.
1.3 Contamination and transmission
Humans are the only natural host and reservoir. The infection is transmitted by ingestion
of food or water contaminated with faeces. Ice cream is recognized as a significant risk
factor for the transmission of typhoid fever. Shellfish taken from contaminated water,
and raw fruit and vegetables fertilized with sewage, have been sources of past outbreaks.
The highest incidence occurs where water supplies serving large populations are
contaminated with faeces. Epidemiological data suggest that waterborne transmission
of
with large inocula and high attack rates over short periods. The inoculum size and the
type of vehicle in which the organisms are ingested greatly influence both the attack
rate and the incubation period. In volunteers who ingested 10
S. typhi usually involves small inocula, whereas foodborne transmission is associated9 and 108 pathogenic
S. typhi
Doses of 10
14 persons who ingested 10
believed that
of
model (10).
Family studies were conducted in Santiago, Chile, during an era of high typhoid
endemicity in order to ascertain whether chronic carriers were significantly more
frequent in households where there were index cases of children with typhoid fever
than in matched control households. Other epidemiological studies investigated whether
in 45 ml of skimmed milk, clinical illness appeared in 98% and 89% respectively.5 caused typhoid fever in 28% to 55% of volunteers, whereas none of3 organisms developed clinical illness. Although it is widelySalmonella is transmitted via the oral route, the transmissionS. typhimurium via the respiratory route has been demonstrated in a mouse
WHO/V&B/03.07 5
risk factors could be identified for persons with typhoid fever in comparison with
uninfected household members. It was concluded that chronic carriers in households
did not play an important role in transmission. Subsequently, it was shown that the
irrigation of salad with wastewater contaminated with sewage was the key factor
responsible for maintaining the high endemicity of typhoid in Santiago. In developed
countries, on the other hand, typhoid is transmitted when chronic carriers contaminate
food as a consequence of unsatisfactory food-related hygiene practices.
WHO/V&B/03.07 7
Chapter 2:
Diagnosis of typhoid fever
The definitive diagnosis of typhoid fever depends on the isolation of
blood, bone marrow or a specific anatomical lesion. The presence of clinical symptoms
characteristic of typhoid fever or the detection of a specific antibody response is
suggestive of typhoid fever but not definitive. Blood culture is the mainstay of the
diagnosis of this disease.
Although ox bile medium (Oxgall) is recommended for enteric fever pathogens
(
diagnostic laboratory, therefore, where other pathogens are suspected, a general blood
culture medium should be used. More than 80% of patients with typhoid fever have
the causative organism in their blood. A failure to isolate the organism may be caused
by several factors: (i) the limitations of laboratory media (11); (ii) the presence of
antibiotics (12); (iii) the volume of the specimen cultured (13); or (iv) the time of
collection, patients with a history of fever for 7 to 10 days being more likely than
others to have a positive blood culture. Bone marrow aspirate culture is the gold standard
for the diagnosis of typhoid fever (14, 15, 16) and is particularly valuable for patients
who have been previously treated, who have a long history of illness and for whom
there has been a negative blood culture with the recommended volume of blood (17).
Duodenal aspirate culture has also proved highly satisfactory as a diagnostic test (18)
but has not found widespread acceptance because of poor tolerance of duodenal
aspiration, particularly in children (19).
S. typhi fromS. typhi and S. paratyphi), only these pathogens can be grown on it. In a general
2.1 Specimens
If a bacteriology laboratory is not available on site, clinical specimens for culture can
be transported to a main laboratory for processing. For blood culture it is essential to
inoculate media at the time of drawing blood. For other specimens it is advisable to
make the time of transportation to the laboratory as short as possible. It is more
important to process the specimens quickly than to keep them cold. Once they have
been inoculated, blood culture bottles should not be kept cold. They should be incubated
at 37°C or, in tropical countries, left at room temperature, before being processed in
the laboratory.
2.1.1 Blood
The volume of blood cultured is one of the most important factors in the isolation of
S. typhi
adults in order to achieve optimal isolation rates; 2
and preschool children (13, 17). This is because children have higher levels of bacteraemia
than adults. In some regions it may be impossible to collect such large volumes of
from typhoid patients: 1015 ml should be taken from schoolchildren and4 ml are required from toddlers
8 The diagnosis, treatment and prevention of typhoid fever
blood and so alternative diagnostic methods may be necessary for cases in which blood
cultures are negative. Because reducing the blood volume reduces the sensitivity of the
blood culture, however, an effort should be made to draw sufficient blood if at all
possible. Blood should be drawn by means of a sterile technique of venous puncture
and should be inoculated immediately into a blood culture bottle with the syringe that
has been used for collection.
Several reports of pseudobacteraemia have been associated with the reinoculation of
blood culture bottles after the collection of blood in contaminated vessels. The practice
of inoculating blood culture bottles from specimens taken for biochemical
or haematological analysis should therefore be avoided. The optimum ratio of the
volume of blood to traditional culture broth should be 1 to 10 or more (e.g. 1:12).
Some commercial blood culture systems have special resins in the media which allow
higher volumes of blood to be used. The instructions with commercial blood culture
systems should always be read and the recommended amounts should not be exceeded.
In general, if 5 ml of blood are drawn they should be inoculated into 45 ml or more of
broth. If 10
and inoculated into two or more blood culture bottles. This allows the use of standard
blood culture bottles of 50 ml. For small children the volume of blood drawn can be
reduced but should still be inoculated into 45 ml of culture broth. In order to assist the
interpretation of negative results the volume of blood collected should be carefully
recorded. The blood culture bottle should then be transported to the main laboratory
at ambient temperature (15°C to 40°C) as indicated above. Blood cultures should not
be stored or transported at low temperatures. If the ambient temperature is below
15°C it is advisable to transport blood cultures in an incubator. In the laboratory, blood
culture bottles should be incubated at 37°C and checked for turbidity, gas formation
and other evidence of growth after 1, 2, 3 and 7 days. For days 1, 2 and 3, only bottles
showing signs of positive growth are cultured on agar plates. On day 7 all bottles
should be subcultured before being discarded as negative.
15 ml of blood are drawn the specimen can be divided into equal aliquots
2.1.2 Serum
For serological purposes, 1
anticoagulant. A second sample, if possible, should be collected at the convalescent
stage, at least 5 days later. After clotting has occurred the serum should be separated
and stored in aliquots of 200 ml at +4°C. Testing can take place immediately or storage
can continue for a week without affecting the antibody titre. The serum should be
frozen at -20°C if longer-term storage is required.
3 ml of blood should be inoculated into a tube without
2.1.3 Stool samples
Stools can be collected from acute patients and they are especially useful for the diagnosis
of typhoid carriers. The isolation of
However, the clinical condition of the patient should be considered. Stool specimens
should be collected in a sterile wide-mouthed plastic container. The likelihood of
obtaining positive results increases with the quantity of stools collected. Specimens
should preferably be processed within two hours after collection. If there is a delay the
specimens should be stored in a refrigerator at 4°C or in a cool box with freezer packs,
and should be transported to the laboratory in a cool box. Stool culture may increase
the yield of culture-positive results by up to 5% in acute typhoid fever. If a stool
sample cannot be obtained, rectal swabs inoculated into Carry Blair transport medium
can been used but these are less successful.
S. typhi from stools is suggestive of typhoid fever.
WHO/V&B/03.07 9
2.2 Microbiological procedures
2.2.1 Blood culture
A typical blood culture bottle contains 45 ml of tryptic soy broth or brain heart infusion
broth. These are inoculated with 5 ml of fresh blood and incubated at 37°C. Negatives
should be kept for at least seven days. Because
found in blood, subculturing is performed on days 1, 2, 3 and 7 on non-selective agar.
The best agar is blood agar (horse or sheep blood) as this allows the growth of most
bacterial pathogens. If blood agar is not available, nutrient agar can be used in
combination with MacKonkey agar. In some laboratories the use of MacConkey agar
alone is preferred as this allows the growth of only bile-tolerant bacteria such as
S. typhi is not the only bacterial pathogen
S. typhi
The contamination of blood cultures reduces isolation rates for
prevented as far as possible. It is important to identify contaminating bacteria that
come from the skin of patients or the air of the laboratory so that measures can be
taken to prevent further problems. MacKonkey agar should therefore not be used as
the only agar for the sampling of blood cultures in a diagnostic microbiology laboratory.
Furthermore, because it is selective, MacKonkey agar does not permit the growth of
Gram-positive pathogens or even all
and does not allow the growth of many Gram-positive contaminants.S. typhi and should beE. coli.
For suspected tyhoid fever, subculture plates should be incubated at 37°C for
18
24 hours in an aerobic incubator.
2.2.2 Stool or rectal swab culture
This involves inoculating 1 g of stool into 10 ml of selenite F broth and incubating at
37°C for 18
instructions should be carefully followed during preparation and overheating of the
broth during sterilization should be avoided. Once a batch is prepared it should be
stored at 4°C. Selenite broth inhibits the motility of
kill this bacterium. A subculture of selenite broth on a selective agar is therefore made
from the surface of the broth without disturbing the sediment. The choice of agar
media includes Mac Conkey agar, desoxycholate citrate agar, xylose-lysinedesoxycholate
agar, and hektoen enteric agar or SS (
incubated at 37°C for 24 hours. Different batches of agar plates can give slightly different
colonies of
quality control for each batch of agar plates and selenite broth. New batches of media
are inoculated with the control strain and the amount of growth and the appearance of
the colonies are recorded. If
medium, discard the medium and make a fresh one.
The identification of colonies as
quality are available. Colonies from solid media can be used for agglutination with
specific antisera. Several salmonellae may share the same antigenic structure.
Consequently, confirmation by means of biochemical tests is always necessary.
48 hours. Because selenite broth is very sensitive to heat the manufacturer’sE. coli found in stools but does notSalmonellaShigella). The plate isS. typhi and it is therefore important to keep one strain of S. typhi for use inS. typhi does not grow as well as usual in any batch ofS. typhi is straightforward if reagents of satisfactory
10 The diagnosis, treatment and prevention of typhoid fever
2.2.3 Colony characteristics
Blood agar
On blood agar,
colonies.
S. typhi and S. paratyphi usually produce non-haemolytic smooth white
MacConkey agar
On MacConkey agar, salmonellae produce lactose non-fermenting smooth colonies.
SS agar
On SS agar, salmonellae usually produce lactose non-fermenting colonies with black
centres (except
S. paratyphi A, whose colonies do not have black centres).
Desoxycholate agar
On desoxycholate agar, salmonellae produce lactose non-fermenting colonies with black
centres (except
S. paratyphi A, whose colonies do not have black centres).
Xylose-lysine-desoxycholate agar
On xylose-desoxycholate agar, salmonellae produce transparent red colonies with black
centres (except
S. paratyphi A, whose colonies do not have black centres).
Hektoen enteric agar
On hektoen enteric agar, salmonellae produce transparent green colonies with black
centres (except
S. paratyphi A, whose colonies do not have black centres).
Bismuth sulfite agar
On this medium, salmonellae produce black colonies.
WHO/V&B/03.07 11
2.2.4 Biochemical identification
Suspected colonies obtained on the above media are screened by means of the following
media/tests:
The production of acid turns the agar yellow. For the slant this means lactose
fermentation and for the butt this means glucose fermentation.
Alk = alkaline, Wk = weak, V= variable result.
2.3 Serological procedures
2.3.1 Serological identification of Salmonella
Salmonellae
latter existing in some serotypes in phases 1 and 2. Some salmonellae also have an
envelop antigen called Vi (virulence). The salmonellae that cause typhoid fever and
paratyphoid fever have the following antigenic compositions and belong to the
serogroups indicated.
can be characterized by their somatic (O) and flagellar (H) antigens, the
-
!
-
! "
#$ %
Antigens in parentheses are either weak or absent in some isolates.
The O antigen is usually determined by means of the slide agglutination test with
group-specific antiserum followed by agglutination with factor antiserum. Growth
from non-selective agar or Kliger’s iron agar can be used for the determination of
O antigen. Strains of
strains non-agglutinable in O antisera. These cultures agglutinate in Vi antiserum.
S. typhi and S. paratyphi C may possess Vi antigen that render the
12 The diagnosis, treatment and prevention of typhoid fever
They will agglutinate in O antiserum, however, after destruction of the Vi antigen by
boiling the culture for 10 minutes. The specific O antigen is confirmed by slide
agglutination with factor antiserum. The specific O antigens for typhoid fever organisms
are shown below.
"#"
#"
"
% #&$
H antigen is usually determined by means of the tube agglutination test. The organisms
should be motile and from a liquid culture. The motility of weakly motile organisms
can be enhanced by repeated passage in liquid cultures. Determination of the O antigen
and the phase 1 H antigen only is usually sufficient for the identification of typhoid
fever organisms and paratyphoid fever organisms. The specific phase 1 antigens for
typhoid fever organisms are shown below. Antisera against these antigens are used,
usually in the tube agglutination test.
-
-
" !
%
In some cultures, only some organisms express phase 1 H antigens and others express
phase 1 and 2 H antigens at the same time. Such cultures agglutinate with both phase 1
and phase 2 antisera. In cultures where a single phase antigen is expressed the antigen
in the other phase can be induced by incubating the culture with antiserum to the
phase antigen being expressed (20).
S. typhi
they are rare.
two serotypes have identical antigens. However, the serotypes can be differentiated
biochemically. The former is tartrate-positive and produces non-typhoid salmonellosis,
and the latter is tartrate-negative and produces typhoid salmonellosis.
considered to be a tartrate-positive variant of
freundii
against d in
Some of the non-typhoidal salmonellae can cause febrile illness that mimics enteric
fever. However, these strains can be differentiated biochemically.
with flagella variant Hj and with phase 2 antigen Z66 have been reported butSalmonella java can be misidentified as S. paratyyphi B because theseS. java is nowS. paratyphi B. S. dublin and Citrobacterpossess Vi antigen. However, the phase 1 H antigens of S. dublin are g, p asS. typhi. Unlike C. freundii, S. typhi does not grow in KCN broth (21).
WHO/V&B/03.07 13
2.3.2 Felix-Widal test
This test measures agglutinating antibody levels against O and H antigens. The levels
are measured by using doubling dilutions of sera in large test tubes. Usually, O antibodies
appear on days 6-8 and H antibodies on days 10-12 after the onset of the disease.
The test is usually performed on an acute serum (at first contact with the patient).
A convalescent serum should preferably also be collected so that paired titrations can
be performed. In practice, however, this is often difficult. At least 1 ml of blood should
be collected each time in order to have a sufficient amount of serum. In exceptional
circumstances the test can be performed on plasma without any adverse effect on the
result.
The test has only moderate sensitivity and specificity. It can be negative in up to 30%
of culture-proven cases of typhoid fever. This may be because of prior antibiotic therapy
that has blunted the antibody response. On the other hand,
H antigens with other
Enterobacteriacae, and this can lead to false-positive results. Such results may also
occur in other clinical conditions, e.g. malaria, typhus, bacteraemia caused by other
organisms, and cirrhosis. In areas of endemicity there is often a low background level
of antibodies in the normal population. Determining an appropriate cut-off for a positive
result can be difficult since it varies between areas and between times in given
areas (22).
It is therefore important to establish the antibody level in the normal population in a
particular locality in order to determine a threshold above which the antibody titre is
considered significant. This is particularly important if, as usually happens, a single
acute sample is available for testing. If paired sera are available a fourfold rise in the
antibody titre between convalescent and acute sera is diagnostic. Quality control of
the test is achieved by running a standard serum with a known antibody titre in parallel
in each batch of assays. The variations in the standard serum should not exceed one
tube, i.e. double dilution.
Despite these limitations the test may be useful, particularly in areas that cannot afford
the more expensive diagnostic methods (23). This is acceptable so long as the results
are interpreted with care in accordance with appropriate local cut-off values for the
determination of positivity. This test is unnecessary if the diagnosis has already been
confirmed by the isolation of
developed.
S. typhi shares O andSalmonella serotypes and has cross-reacting epitopes with otherS. typhi from a sterile site. New diagnostic tests are being
2.3.3 New diagnostic tests: current status and usefulness
There is a need for a quick and reliable diagnostic test for typhoid fever as an alternative
to the Widal test. Recent advances include the IDL Tubex
company, which reportedly can detect IgM O9 antibodies from patients within a few
minutes. Another rapid serological test, Typhidot
It was developed in Malaysia for the detection of specific IgM and IgG antibodies
against a 50 kD antigen of
recently developed to detect specific IgM antibodies only. The dipstick test, developed
in the Netherlands, is based on the binding of
to
an anti-human IgM antibody conjugated to colloidal dye particles.
® test marketed by a Swedish®, takes three hours to perform.S. typhi. A newer version of the test, Typhidot-M®, wasS. typhi-specific IgM antibodies in samplesS. typhi lipopolysaccharide (LPS) antigen and the staining of bound antibodies by
14 The diagnosis, treatment and prevention of typhoid fever
IDL Tubex® test
The Tubex
two minutes). It exploits the simplicity and user-friendliness of the Widal and the
slide latex agglutination tests but uses the separation of coloured particles in
solution to improve resolution and sensitivity. Specificity is improved by means of an
inhibition assay format and by detecting antibodies to a single antigen in
The O9 antigen used in the test is extremely specific because its immunodominant
epitope is a very rare dideoxyhexose sugar that occurs in nature. This antigen has been
found in serogroup D
the tyvelose antigen found in
do not cross-react with each other. A positive result given by Tubex
a
responsible. Infections caused by other serotypes, including
results.
Immunogenically, the O9 antigen is immunodominant and robust. Unlike the capsular
(Vi) and flagellar antigens that are thymus-independent type II in nature and poorly
immunogenic in infants, the O9 antigen (or LPS in general) is thymus-independent
type I, immunogenic in infants, and a potent B cell mitogen. It can stimulate B cells
without the help of T cells (unlike protein antigens) and, consequently, anti-O9
responses are rapid. This is important teleologically, as they form the first line of host
defence. For reasons yet to be elucidated, Tubex
This makes it invaluable as an aid in the diagnosis of current infections.
The test pack includes: 1) sets of specially-designed V-shaped tubes that allow six samples
per set to be examined simultaneously; 2) reagent A, comprising magnetic particles
coated with
with a monoclonal antibody specific for the O9 antigen. The reagents are stable for
over a year at 4°C, and for at least some weeks at ambient temperature.
A drop of test serum is mixed for about one minute with a drop of reagent A in the
tube. Two drops of reagent B are then added and the contents are mixed thoroughly
for 1
which they are slid several times. The result, which can be read immediately or up to
many hours later, is based on the colour of the reaction mixture. A range of colours
involving varying proportions of redness and blueness can be expected, and a colour
chart is provided for the purpose of scoring. Red indicates negativity while increasing
blueness denotes increasing positivity.
The rationale of the test is as follows. If the serum is negative for O9 antibodies the
antibody-coated indicator particles bind to the antigen-coated magnetic beads.
When a magnet is applied, the magnetic particles settle to the bottom of the tube together
with any blue indicator particles associated with these. Consequently a background
red colour is left in the solution. This background colour is actually exploited to
camouflage the sample colour of haemolysed sera. If, on the other hand, the patient’s
serum contains O9 antibodies, these bind to the magnetic particles and prevent the
indicator particles from binding to them. The indicator particles thus remain suspended
and the resultant colour of the solution is blue.
® test is simple (essentially a one-step test) and rapid (taking approximatelyS. typhi only.salmonellae but not in other microorganisms. The closest to it isTrichinella spiralis but antibodies to these two antigens® invariably suggestsSalmonella infection, although the test cannot tell which group D Salmonella isS. paratyphi A, give negative® detects IgM antibodies but not IgG.S. typhi LPS; 3) reagent B, comprising blue-coloured latex particles coated2 minutes. The set of tubes is then placed on a magnet-embedded stand, across
WHO/V&B/03.07 15
Typhidot
® test
This test makes use of the 50 kD antigen to detect specific IgM and IgG antibodies to
S. typhi
value (26, 27, 28). This dot EIA test offers simplicity, speed, specificity (75%), economy,
early diagnosis, sensitivity (95%) and high negative and positive predictive values.
The detection of IgM reveals acute typhoid in the early phase of infection, while the
detection of both IgG and IgM suggests acute typhoid in the middle phase of infection.
In areas of high endemicity where the rate of typhoid transmission is high the detection
of specific IgG increases. Since IgG can persist for more than two years after typhoid
infection (29) the detection of specific IgG cannot differentiate between acute and
convalescent cases. Furthermore, false-positive results attributable to previous infection
may occur. On the other hand, IgG positivity may also occur in the event of current
reinfection. In cases of reinfection there is a secondary immune response with a
significant boosting of IgG over IgM, such that the latter cannot be detected and its
effect is masked. A possible strategy for solving these problems is to enable the detection
of IgM by ensuring that it is unmasked (30). In order to increase diagnostic accuracy in
these situations the original Typhidot
the serum sample. Studies with the modified test, Typhidot-M
inactivation of IgG removes competitive binding and allows access of the antigen to
the specific IgM when it is present. The detection of specific IgM within three hours
suggests acute typhoid infection. Evaluations of Typhidot
settings showed that they performed better than the Widal test and the culture
method (30).
In laboratory diagnoses of typhoid fever the method used as the gold standard should
approach 100% in sensitivity, specificity and positive and negative predictive values.
Evaluation studies have shown that Typhidot-M
(28). Although culture remains the gold standard it cannot match Typhidot-M
sensitivity (>93%), negative predictive value and speed (28). Typhidot-M
the Widal test when used in conjunction with the culture method for the rapid and
accurate diagnosis of typhoid fever. The high negative predictive value of the test suggests
that Typhidot-M
(25). It has undergone full-scale multinational clinical evaluation of its diagnostic® test was modified by inactivating total IgG in®, have shown that® and Typhidot-M® in clinical® is superior to the culture method® in® can replace® would be useful in areas of high endemicity.
IgM dipstick test
The typhoid IgM dipstick assay is designed for the serodiagnosis of typhoid fever
through the detection of
samples.
The assay consists of a dipstick, a lyophilized non-enzymatic detection reagent, liquid
to reconstitute the detection reagent, liquid to wet the test strip of the dipstick before
incubation with serum and detection reagent, and test tubes. The components are stable
for two years if stored in the temperature range 4-25°C in a dry place and protected
from direct exposure to sunlight.
Tubex
preliminary study involving stored sera the test performed better than the Widal test in
both sensitivity and specificity (24).
S. typhi-specific IgM antibodies in serum or whole blood® has not been evaluated extensively but several trials are being planned. In a
16 The diagnosis, treatment and prevention of typhoid fever
The assay is based on the binding of
antigen and the staining of bound antibodies by an anti-human IgM antibody conjugated
to colloidal dye particles. The white test strip of the dipstick contains the antigen
immobilized in a distinct line. The strip also has a control line with anti-human
IgM antibodies.
The assay is performed by incubation of the wetted test strip in a mixture of serum and
detection reagent, the serum being diluted at 1:50 in the detection reagent. Whole blood
may be tested at a 1:25 dilution in detection reagent. The incubation period is three
hours at room temperature. When incubation is complete the test strip is rinsed
thoroughly with water and then allowed to dry. The result is read by visual inspection
of the test strip for staining of the antigen and control lines. The test result is scored
negative if no staining of the antigen line occurs and is graded 1+, 2+, 3+ or 4+ if there
is weak, moderate strong or very strong staining as indicated by comparison with a
coloured reference strip. The control line should stain in all runs.
Evaluations of the dipstick test in laboratory-based studies in Indonesia (31, 32),
Kenya (33), Viet Nam (33) and Egypt (34) have shown consistent results. These studies
indicated sensitivities of 65% to 77% for samples collected at the time of first
consultation from culture-confirmed patients and specificities of 95% to 100%. The
results of culture and serological investigation may be influenced by various factors,
among them the time of sample collection and the use of antibiotics before consultation
and sample collection. In a study conducted in Makassar, Indonesia, the sensitivity of
the blood culture method was estimated to be 66%, and that of the dipstick test
calculated for the combined group of culture-confirmed and culture-negative patients
with a final clinical diagnosis of typhoid fever was 48%. The sensitivity ranged from
29% for samples collected during the first week of illness to 96% for samples collected
at a later stage. Tests on follow-up samples showed seroconversion in the majority of
the dipstick-negative typhoid patients.
The dipstick test provides a rapid and simple alternative for the diagnosis of typhoid
fever, particularly in situations where culture facilities are not available. The assay can
be performed by people without formal training and in the absence of specialized
equipment. Electricity is not required, as the components can be stored without cooling.
The results of the dipstick test can be obtained on the day when patients present.
This makes prompt treatment possible. Specific antibodies usually only appear a week
after the onset of symptoms and signs. This should kept in mind when a negative
serological test result is being interpreted.
S. typhi-specific IgM antibodies to S. typhi LPS
2.4 Antimicrobial susceptibility test for typhoid fever organisms
Antimicrobial susceptibility testing is crucial for the guidance of clinical management.
Isolates from many parts of the world are now multidrug-resistant (MDR) (35, 36, 37).
Isolates are usually resistant to ampicillin, chloramphenicol, sulfonamide, trimethoprim,
streptomycin and tetracycline. Alternative drugs that are used for treatment include:
fluoroquinolones (e.g. ciprofloxacin), third-generation cephalosporins (e.g. ceftriaxone,
cefotaxime), a monobactum beta-lactam (aztreonam) and a macrolide (azithromycin).
Even though resistance to the first two has been noted they nevertheless remain useful
(38). Reduced susceptibility to fluoroquinolones is indicated by in vitro resistance to
nalidixic acid (39).
WHO/V&B/03.07 17
In vitro susceptibility testing usually involves disc diffusion. The choice of antimicrobial
agents for the test is dictated by the agents that are currently being used for treatment
and the desire to determine the prevalence of MDR strains. After the previous firstline
drugs were discontinued for the treatment of typhoid fever in Bangladesh because
of the emergence of MDR strains, the prevalence of multidrug resistance decreased
and the possibility arose of using these drugs again (40). It is therefore recommended
that susceptibility tests be performed against the following antimicrobial agents: a
fluoroquinolone, a third-generation cephalosporin and any other drug currently used
for treatment, nalidixic acid (for determining reduced susceptibility to fluoroquinolones
because of the possibility of false in vitro susceptibility against the fluoroquinolone
used for treatment), and the previous first-line antimicrobials to which the strains could
be resistant (chloramphenicol, ampicillin, trimethoprim/sulfamethoxazole,
streptomycin and tetracycline). Azithromycin disc test results should be interpreted
with caution. The appropriate break-point recommendations for azithromycin against
S. typhi
isolates are intermediate according to current guidelines.
are still not clear. Patients may respond satisfactorily to azithromycin even if
2.5 Storage of typhoid fever organisms
The isolates can be stored for up to two to three years on a nutrient agar, e.g. trypticase
soy agar. The butt is stabbed and the slant is streaked and incubation takes place at
37°C for 18
cork with parafilm or dipping the cork in melted paraffin. Alternatively, sterile mineral
oil is poured on to cover the growth in the slant and the tube is corked. The tube is
stored at room temperature, preferably between 20°C and 22°C, away from light in a
closed cupboard. There is a risk that plasmids encoding antimicrobial resistance or
other properties can be lost from isolates stored in this way.
Isolates can be stored for several years by freeze-drying, inoculating a thick suspension
of growth in a nutrient broth (e.g. trypticase soy broth) with 15% glycerol in a cryovial,
10% skim milk in a cryovial, or a cryovial with beads, and freezing the vial at -70°C.
Plasmids in isolates stored by these methods are stable. The use of a cryovial with
beads has the advantage that beads can be removed for subculture without thawing the
culture.
24 hours. The tube is corked and made airtight by either covering the
2.6 Quality control
The steps involved in the accurate laboratory diagnosis of typhoid fever include
specimen collection and transport, the performance of laboratory procedures, and
reporting. It is important that the correct specimen is collected in the correct volume,
that it is transported to the laboratory in the right condition, that correct laboratory
procedures are followed and that reporting is accurate. These steps should therefore be
monitored at all levels and correction should take place if unacceptable performance is
identified. Quality assurance is vital to the success of such investigations.
Quality control programmes ensure that the information generated by laboratories
is accurate, reliable and reproducible. This is accomplished by assessing the quality
of specimens and monitoring the performance of test procedures, reagents, media,
instruments, and personnel. Laboratories should have internal quality control
programmes. A panel of reference isolates consisting of typhoid and non-typhoid
salmonellae and other Enterobacteriaceae should be maintained. At periodic intervals,
18 The diagnosis, treatment and prevention of typhoid fever
e.g. monthly, the laboratory supervisor should submit a random selection of the
reference isolates under code to laboratory technologists for evaluation. Quality control
of the disc susceptibility test should take place.
parallel with the test strains. The susceptibility zones for the reference strain against
various antimicrobials should be within the acceptable ranges. The results of these
evaluations should be entered in a quality control monitoring book. Appropriate
measures should be taken to solve any problems that are encountered.
It is desirable to participate in external quality control programmes whenever possible.
It should be noted that this is relatively expensive and that there could be problems
relating to the timely transport of quality control specimens to certain countries because
of uncertainties about carriers and customs.
It is important to confirm
possibility of their misidentification.
E. coli ATCC 25922 should be run inSalmonella isolates in a reference laboratory because of the
WHO/V&B/03.07 19
Chapter 3:
Treatment of typhoid fever
3.1 General management
Supportive measures are important in the management of typhoid fever, such as oral or
intravenous hydration, the use of antipyretics, and appropriate nutrition and blood
transfusions if indicated. More than 90% of patients can be managed at home with oral
antibiotics, reliable care and close medical follow-up for complications or failure to
respond to therapy (41). However, patients with persistent vomiting, severe diarrhoea
and abdominal distension may require hospitalization and parenteral antibiotic therapy.
3.2 Antimicrobial therapy
Efficacy, availability and cost are important criteria for the selection of first-line
antibiotics to be used in developing countries. This section reviews the therapeutic
guidelines for the treatment of typhoid fever across all age groups. It should be noted,
however, that therapeutic strategies for children, e.g. the choice of antibiotics, the dosage
regimen and the duration of therapy, may differ from those for adults.
The fluoroquinolones are widely regarded as optimal for the treatment of typhoid
fever in adults (42). They are relatively inexpensive, well tolerated and more rapidly
and reliably effective than the former first-line drugs, viz. chloramphenicol, ampicillin,
amoxicillin and trimethoprim-sulfamethoxazole (Table 1). The majority of isolates are
still sensitive. The fluoroquinolones attain excellent tissue penetration, kill
its intracellular stationary stage in monocytes/macrophages and achieve higher active
drug levels in the gall bladder than other drugs. They produce a rapid therapeutic
response, i.e. clearance of fever and symptoms in three to five days, and very low rates
of post-treatment carriage (43, 44). Evidence from various settings in Asia indicates
that the fluoroquinolones are equally effective in the treatment of typhoid fever in
children
However, the emergence of MDR strains has reduced the choice of antibiotics in many
areas. There are two categories of drug resistance: resistance to antibiotics such as
chloramphenicol, ampicillin and trimethoprim-sulfamethoxazole (MDR strains)
and resistance to the fluoroquinolone drugs. Resistance to the fluoroquinolones may
be total or partial. The so-called nalidixic-acid-resistant
of reduced susceptibility to fluoroquinolones compared with nalidixic-acid-sensitive
strains. Nalidixic acid itself is never used for the treatment of typhoid. These isolates
are susceptible to fluoroquinolones in disc sensitivity testing according to current
guidelines. However, the clinical response to treatment with fluoroquinolones of
nalidixic-acid-resistant strains is significantly worse than with nalidixic-acid-senstive
strains. There is a significant number of MDR strains from the Indian subcontinent
S. typhi inS. typhi (NARST) is a marker
20 The diagnosis, treatment and prevention of typhoid fever
and some other Asian countries (not Indonesia).
problem in Kenya. Nalidixic-acid-resistant strains are now endemic in many areas of
Viet Nam and have also been reported from the Indian subcontinent and Tajikistan.
There are disturbing recent reports of the emergence of fluorquinolone-resistant isolates
in various parts of Asia (45, 46, 47) and there have been a few reports of resistance to
third-generation cephalopsorins in the same region. Reassuringly, however, many of
these reports are coupled with evidence of the re-emergence of sensitive isolates in the
same regions. Table 1 outlines the treatment strategies for uncomplicated typhoid.
S. typhi has recently emerged as a
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a
Three-day courses are also effective and are particularly so in epidemic containment.
b
the third-generation cephalosporins, or a 10
Combinations of these are now being evaluated.
The optimum treatment for quinolone-resistant typhoid fever has not been determined. Azithromycin,14 day course of high-dose fluoroquinolones, is effective.
The available fluoroquinolones (ofloxacin, ciprofloxacin, fleroxacin, perfloxacin)
are highly active and equivalent in efficacy (with the exception of norfloxacin which
has inadequate oral bioavailability and should not be used in typhoid fever).
The fluoroquinolone drugs are generally very well tolerated. However, in some countries
the use of fluoroquinolones is relatively contraindicated in children because of concerns
that they may cause articular damage. These agents are not registered for routine use in
children. The concerns have arisen because of evidence of articular damage in growing,
weight-bearing joints in beagles (48). There is now extensive experience in the use of
these drugs in large numbers of children with a variety of conditions, often with longterm
follow-up (cystic fibrosis, typhoid), and in the extensive use of short courses of
fluoroquinolones in children for the treatment of both typhoid fever and bacillary
dysentery (49). Their considerable benefits, particularly in areas where there are no
affordable oral alternatives, outweigh the putative risk. The only known articular sideeffect
is Achilles tendon rupture in patients who are also taking corticosteroids, and
this has been reported only rarely.
Ciprofloxacin, ofloxacin, perfloxacin and fleroxacin have generally proved effective.
In recent years, however, there have been many reports of reduced susceptibility and
treatment failure for ciprofloxacin (50, 51). No evidence of toxicity and impact on
growth has been described in children with typhoid who have received ciprofloxacin
(49). There is no evidence of the superiority of any particular fluoroquinolone. Nalidixic
acid and norfloxacin do not achieve adequate blood concentrations after oral
WHO/V&B/03.07 21
administration and should not be used. For nalidixic-acid-sensitive
regimens have proved highly effective. Courses of treatment of three and five days
have also proved highly effective against nalidixic-acid-sensitive strains. These very
short courses are best reserved for outbreaks when antibiotics are in short supply.
For nalidixic-acid-resistant infections a minimum of seven days of treatment at the
maximum permitted dosage is necessary and 10
shorter than seven days are unsatisfactory.
Chloramphenicol, despite the risk of agranulocytosis in 1 per 10 000 patients,
is still widely prescribed in developing countries for the treatment of typhoid fever
(52, 53, 54).
and Asia, remain sensitive to this drug and it is widely available in most primary care
settings in developing countries for the treatment of pneumonia.
The disadvantages of using chloramphenicol include a relatively high rate of relapse
(5
state in adults. The recommended dosage is 50
into four doses per day (54), or for at least five to seven days after defervescence.
The usual adult dose is 500 mg given four times a day. Oral administration gives slightly
greater bioavailability than intramuscular (i.m.) or intravenous (i.v.) administration of
the succinate salt.
Ampicillin and amoxicillin are used at 50 to 100 mg per kg per day orally, i.m. or i.v.,
divided into three or four doses. No benefit has been reported to result from the addition
of clavulanic acid to amoxicillin.
Trimethoprim-sulfamethoxazole, (TMP
dose of 160 mg TMP plus 800 mg SMZ twice daily or in children at 4 mg TMP per kg
and 20 mg SMZ per kg for 14 days (55).
Of the third-generation cephalosporins, oral cefixime (15
adults, 100
geographical settings and found to be satisfactory (56, 57, 58). However, a trial of
cefixime in MDR typhoid in Viet Nam indicated significantly higher treatment failure
rates than with ofloxacin (59). Other agents, e.g. cefodoxime, have proved successful
against typhoid fever (60). Because of the rising rates of quinolone resistance (61)
there is a clear need to identify improved strategies for treating MDR typhoid in
childhood. Recent data on the use of azithromycin in children indicate that it may be
safely given as an alternative agent for the treatment of uncomplicated typhoid
fever (62).
Azithromycin in a dose of 500 mg (10 mg/kg) given once daily for seven days has
proved effective in the treatment of typhoid fever in adults and children with
defervescence times similar to those reported for chloramphenicol. A dose of 1 g
per day for five days was also effective in adults (42).
If intravenous antibiotics are required, i.v. cephalosporins can be given in the following
doses: ceftriaxone, 50
two doses; cefotaxime, 40
three doses; and cefoperazone, 50-100 mg per kg per day (2
in two doses. Ciprofloxacin, ofloxacin and pefloxacin are also available for i.v. use.
S. typhi, seven-day14 days are usually required. CoursesS. typhi strains from many areas of the world, e.g. most countries in Africa7%), long treatment courses (14 days) and the frequent development of a carrier75 mg per kg per day for 14 days dividedSMZ) can be used orally or i.v. in adults at a20 mg per kg per day for200 mg twice daily) has been widely used in children in a variety of75 mg per kg per day (24 g per day for adults) in one or80 mg per kg per day (24 g per day for adults) in two or4 g per day for adults)
22 The diagnosis, treatment and prevention of typhoid fever
There are few data on the treatment of typhoid in pregnancy. The beta-lactams are
considered safe (63). There have been several case reports of the successful use of
fluoroquinolones but these have generally not been recommended in pregnancy because
of safety concerns (64, 65). Ampicillin is safe in pregnant or nursing women, as is
ceftriaxone in such women with severe or MDR disease. Although there are no data
indicating that azithromycin is unsafe for pregnant or nursing women, alternatives
should be used if available.
Most of the data from randomized controlled trials relate to patients treated in regions
of endemicity. There are few data from such trials relating to patients treated in regions
where the disease is not endemic or to returning travellers. Knowledge of the antibiotic
sensitivity of the infecting strain is crucial in determining drug choice. If no culture is
available a knowledge of likely sensitivity as indicated by the available global data may
be useful.
The evidence suggests that the fluoroquinolones are the optimal choice for the treatment
of typhoid fever in adults and that they may also be used in children. The recent
emergence of resistance to fluoroquinolones, however, suggests that their widespread
and indiscriminate use in primary care settings should be restricted. In areas of the
world where the fluoroquinolones are not available or not registered for public health
use and where the bacterium is still fully sensitive to traditonal first-line drugs
(chloramphenicol, amoxicillin or trimethoprim-sulfamethoxazole), these remain
appropriate for the treatment of typhoid fever. They are inexpensive, widely available
and rarely associated with side-effects.
3.3 Management of complications
Both outpatients and inpatients with typhoid fever should be closely monitored for
the development of complications. Timely intervention can prevent or reduce morbidity
and mortality. The parenteral fluoroquinolones are probably the antibiotics of choice
for severe infections but there have been no randomized antibiotic trials (66). In severe
typhoid the fluoroquinolones are given for a minimum of 10 days (Table 2). Typhoid
fever patients with changes in mental status, characterized by delirium, obtundation
and stupor, should be immediately evaluated for meningitis by examination of the
cerebrospinal fluid. If the findings are normal and typhoid meningitis is suspected,
adults and children should immediately be treated with high-dose intravenous
dexamethasone in addition to antimicrobials (67). If dexamethasone is given in an initial
dose of 3 mg/kg by slow i.v. infusion over 30 minutes and if, after six hours, 1 mg/kg is
administered and subsequently repeated at six-hourly intervals on seven further
occasions, mortality can be reduced by some 80
Hydrocortisone in a lower dose is not effective (68). High-dose steroid treatment can
be given before the results of typhoid blood cultures are available if other causes of
severe disease are unlikely.
90% in these high-risk patients.
WHO/V&B/03.07 23
Patients with intestinal haemorrhage need intensive care, monitoring and blood
transfusion. Intervention is not needed unless there is significant blood loss.
Surgical consultation for suspected intestinal perforation is indicated. If perforation is
confirmed, surgical repair should not be delayed longer than six hours. Metronidazole
and gentamicin or ceftriazone should be administered before and after surgery if a
fluoroquinolone is not being used to treat leakage of intestinal bacteria into the
abdominal cavity. Early intervention is crucial, and mortality rates increase as the delay
between perforation and surgery lengthens. Mortality rates vary between 10% and
32% (69).
Relapses involving acute illness occur in 5
apparently been treated successfully. A relapse is heralded by the return of fever soon
after the completion of antibiotic treatment. The clinical manifestation is frequently
milder than the initial illness. Cultures should be obtained and standard treatment
should be administered. In the event of a relapse the absence of schistosomiasis should
be confirmed.
20% of typhoid fever cases that have
3.4 Management of carriers
An individual is considered to be a chronic carrier if he or she is asymptomatic and
continues to have positive stool or rectal swab cultures for
recovery from acute illness. Overall, some 1
chronic carriers. The rate of carriage is slightly higher among female patients,
patients older than 50 years, and patients with cholelithiasis or schistosomiasis.
If cholelithiasis or schistosomiasis is present the patient probably requires
cholecystectomy or antiparasitic medication in addition to antibiotics in order to achieve
bacteriological cure. In order to eradicate
(100 mg per kg per day) plus probenecid (Benemid
children)or TMP-SMZ (160 to 800 mg twice daily) is administered for six weeks; about
60% of persons treated with either regimen can be expected to have negative cultures
on follow-up. Clearance of up to 80% of chronic carriers can be achieved with the
administration of 750 mg of ciprofloxacin twice daily for 28 days or 400 mg of
norfloxacin. Other quinolone drugs may yield similar results (70, 71).
S. typhi a year following5% of typhoid fever patients becomeS. typhi carriage, amoxicillin or ampicillin®) (1 g orally or 23 mg per kg for
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24 The diagnosis, treatment and prevention of typhoid fever
Carriers should be excluded from any activities involving food preparation and serving,
as should convalescent patients and any persons with possible symptoms of typhoid
fever. Although it would be difficult for typhoid carriers in developing countries to
follow this recommendation, food handlers should not resume their duties until they
have had three negative stool cultures at least one month apart.
Vi antibody determination has been used as a screening technique to identify carriers
among food handlers and in outbreak investigations. Vi antibodies are very high in
chronic
S. typhi carriers (72).
WHO/V&B/03.07 25
Chapter 4:
Prevention of typhoid fever
The major routes of transmission of typhoid fever are through drinking water or eating
food contaminated with
safe water and by promoting safe food handling practices. Health education is
paramount to raise public awareness and induce behaviour change.
Salmonella typhi. Prevention is based on ensuring access to
4.1 Safe water
Typhoid fever is a waterborne disease and the main preventive measure is to ensure
access to safe water. The water needs to be of good quality and must be sufficient to
supply all the community with enough drinking water as well as for all other domestic
purposes such as cooking and washing.
During outbreaks the following control measures are of particular interest:
strengthened from catchment to consumer. Safe drinking water should be made
available to the population trough a piped system or from tanker trucks.
In urban areas, control and treatment of the water supply systems must be
In rural areas, wells must be checked for pathogens and treated if necessary.
the water however safe its source. Drinking-water can be made safe by boiling it
for one minute or by adding a chlorine-releasing chemical. Narrow-mouthed pots
with covers for storing water are helpful in reducing secondary transmission of
typhoid fever. Chlorine is ineffective when water is stored in metallic containers.
At home, a particular attention must be paid to the disinfection and the storage of
camps, fuel for boiling water and storage containers may have to be supplied.
In some situations, such as poor rural areas in developing countries or refugee
4.2 Food safety
Contaminated food is another important vehicle for typhoid fever transmission.
Appropriate food handling and processing is paramount and the following basic hygiene
measures must be implemented or reinforced during epidemics:
washing hands with soap before preparing or eating food;
avoiding raw food, shellfish, ice;
eating only cooked and still hot food or re-heating it.
26 The diagnosis, treatment and prevention of typhoid fever
During outbreaks, food safety inspections must be reinforced in restaurants and for
street food vendors activities .
Typhoid can be transmitted by chronic carriers who do not apply satisfactory
food-related hygiene practices. These carriers should be excluded from any activities
involving food preparation and serving. They should not resume their duties until they
have had three negative stool cultures at least one month apart.
4.3 Sanitation
Proper sanitation contributes to reducing the risk of transmission of all diarrhoeal
pathogens including
Salmonella typhi.
community. In an emergency, pit latrines can be quickly built.
Appropriate facilities for human waste disposal must be available for all the
implemented
Collection and treatment of sewage, especially during the rainy season, must be
fertilisers must be discouraged.
In areas where typhoid fever is known to be present, the use of human excreta as
4.4 Health education
Health education is paramount to raise public awareness on all the above mentioned
prevention measures. Health education messages for the vulnerable communities need
to be adapted to local conditions and translated into local languages. In order to reach
communities, all possible means of communication (e.g. media, schools, women’s groups,
religious groups) must be applied.
Community involvement is the cornerstone of behaviour change with regard to hygiene
and for setting up and maintenance of the needed infrastructures.
In health facilities, all staff must be repeatedly educated about the need for :
excellent personal hygiene at work;
isolation measures for the patient;
disinfection measure.
4.5 Vaccination
4.5.1 Currently available vaccines
The old parenteral killed whole-cell vaccine was effective but produced strong
side-effects because of LPS. Two safe and effective vaccines are now licensed and
available. One is based on defined subunit antigens, the other on whole-cell live
attenuated bacteria.
WHO/V&B/03.07 27
The first of these vaccines, containing Vi polysaccharide, is given in a single dose
subcutaneous (s.c.) or i.m. Protection begins seven days after injection, maximum
protection being reached 28 days after injection when the highest antibody concentration
is obtained. In field trials conducted in Nepal and South Africa, where the disease is
endemic and attack rates reach 900/100 000, the protective efficacy was 72% one and
half years after vaccination (74) and was still 55% three years after a single dose (75).
The vaccine is approved for persons aged over two years. Revaccination is recommended
every three years for travellers. In a field trial in South Africa, 10 years after
immunization 58% of vaccinees still had over 1 ìg/ml of anti-Vi antibodies in their
blood (76), i.e. a protective level. In efficacy trials conducted in Chiang Su and Guangxi,
China, in 1995 and 1997 respectively with a locally produced Vi vaccine, 72% protection
was obtained in vaccinees (77, 78). A protective efficacy of 70% was reported in a
population vaccinated before or during an outbreak situation in the same country (78).
The Vi vaccine is licensed in Australia and in more than 92 countries in Africa, the
Americas, Asia, and Europe. It is mainly used by travellers visiting areas at high risk of
typhoid fever because of the presence of multidrug-resistant strains. There have been a
few reports of Vi-negative
from the blood of patients have always been Vi-positive. During laboratory storage or
transfer the Vi capsule may be lost but even if this happens through gene mutation or
alteration it is quite uncommon. Moreover, this is not a major problem in relation to
the protection obtained in Asian countries where Vi-negative strains have been reported
at the low average level of 3%. The majority of the 600 000 estimated deaths per year
are in Asia. Vaccinated people with Vi can be differentiated from
of the higher level of Vi antibodies in the latter (see 3.4 above).
The live oral vaccine Ty2la is available in enteric-coated capsule (80) or liquid
formulation. It should be taken in three doses two days apart on an empty stomach.
It elicits protection as from 10
children aged at least 5 years. Travellers should be revaccinated annually. The protective
efficacy of the enteric-coated capsule formulation seven years after the last dose is still
62% in areas where the disease is endemic; the corresponding figure for the liquid
formulation is 70%. Herd immunity was clearly demonstrated during field trials in
Chile. Antibiotics should be avoided for seven days before or after the immunization
series. This vaccine is licensed in 56 countries in Africa, Asia, Europe, South America,
and the USA. Although the package insert allows simultaneous administration of
mefloquine (Lariam
it is recommended that an interval of three days be maintained between the completion
of the immunization series and the first dose of mefloquine or proguanil.
S. typhi strains (79). However, S. typhi strains freshly isolatedS. typhi carriers because14 days after the third dose. It is approved for use in®) or chloroquine (Nivaquine® or Aralen®) for malaria prophylaxis,
4.
5.2 Future vaccines
Vi-rEPA
A new Vi conjugate candidate vaccine bound to non-toxic recombinant
aeruginosa
children aged 5
2
aged 2
No serious side-reactions were observed. The efficacy after 27 months of active
surveillance was 91.2%. Passive surveillance in the 16 months since the study ended
(three-and-a-half years after the first injection) showed 88% efficacy.
Pseudomonasexotoxin A (rEPA) has enhanced immunogenicity in adults and in14 years, and has induced a booster response in children aged4 years (81). In a double-blind randomized field trial, 11 091 Vietnamese children5 years were given two injections of Vi-rEPA separated by six weeks (82).
28 The diagnosis, treatment and prevention of typhoid fever
S. paratyphi
composed of inactivated
A causes the second commonest enteric fever in Asia. The TAB vaccine,Salmonella, caused a strong side-reaction. A new S. paratyphi
A vaccine composed of the surface O-specific polysaccharide conjugated with tetanus
toxoid was shown to be safe and immunogenic in Vietnamese adults, 108 teenagers and
110 children aged 2
4 years (83). An efficacy trial is being planned.
Other candidates
Three live attenuated candidate vaccines are currently being evaluated. Each is
administered as a single oral dose. CVD 908-htrA is an
deletion in the
to produce Vi antigen according to constitutive expression. The second candidate is an
S. typhi strain with a mutationhtrA gene (84, 85); a derivative strain, CVD 909, was prepared in order
S. typhi
The third is a derivative of an
genes
Ty2 strain with triple mutation deletion in the cya, crp and cdt genes (86).S. typhi Ty2 strain with a double mutation deletion inphoP and phoQ (87).
4.
5.3 Recommendations on vaccine use
The occurrence of
the need to use safe and effective vaccines to prevent typhoid fever. WHO recommends
vaccination for people travelling in high-risk areas where the disease is endemic.
People living in such areas, people in refugee camps, microbiologists, sewage workers
and children should be the target groups for vaccination.
S. typhi strains that are resistant to fluoroquinolones emphasizes | |