Typhoid Fever
Description
Typhoid fever is an acute, life-threatening febrile
illness caused by the bacterium Salmonella enterica Typhi.
Occurrence
An estimated 16 million cases of typhoid fever and
600,000 related deaths occur worldwide each year. Approximately 2.6
cases of typhoid fever were reported to the Centers for Disease Control
and Prevention per 1 million U.S. citizens and residents traveling
abroad during the period 1992–1994.
Risk for Travelers
Typhoid vaccination is not required for international
travel, but it is recommended for travelers to areas where there
is a recognized risk of exposure to S. Typhi. Risk is greatest
for travelers to the Indian subcontinent and other low-income countries
(in Asia, Africa, and Central and South America) who will have prolonged
exposure to potentially contaminated food and drink. Vaccination
is particularly recommended for those who will be traveling in smaller
cities, villages, and rural areas off the usual tourist itineraries.
Travelers should be cautioned that typhoid vaccination is not 100%
effective and is not a substitute for careful selection of food and
drink.
Clinical Presentation
The hallmark of infection is persistent, high fevers.
Other common symptoms and signs include headache, malaise, anorexia,
splenomegaly, and relative bradycardia. Many mild and atypical infections
occur.
Prevention
Vaccine
Two typhoid vaccines are currently available for
use in the United States: an oral, live, attenuated vaccine (Vivotif
Berna vaccine, manufactured from the Ty21a strain of S. Typhi
by the Swiss Serum and Vaccine Institute) and a Vi capsular polysaccharide
vaccine (ViCPS) (Typhim Vi, manufactured by Aventis Pasteur) for
intramuscular use. Both vaccines have been shown to protect 50%–80%
of recipients. The intramuscular heat-phenol-inactivated vaccine
(manufactured by Wyeth-Ayerst) has been discontinued. Table
3–18 provides information on vaccine dosage
and administration. The time required for primary vaccination differs
for each of the two vaccines, and each has a different lower age
limit for use in children.
Primary vaccination with oral Ty21a vaccine consists
of a total of four capsules, one taken every other day. The capsules
should be kept refrigerated (not frozen), and all four doses must
be taken to achieve maximum efficacy. Each capsule should be taken
with cool liquid no warmer than 37° C (98.6° F), approximately
1 hour before a meal. This regimen should be completed 1 week before
potential exposure. The vaccine manufacturer recommends that Ty21a
not be administered to infants or children <6 years of age. Primary
vaccination with ViCPS consists of one 0.5-mL (25-µg) dose administered
intramuscularly. The manufacturer does not recommend the vaccine
for infants <2 years of age. (See “Vaccine
Recommendations for Infants and Children,” “Typhoid
Vaccine,”, for a discussion of typhoid immunization
for infants who will be traveling.) One dose of vaccine should be
given at least 2 weeks before expected exposure. Current recommendations
for revaccination are provided in Table
3–18.
Adverse Reactions
Information on adverse reactions is presented in Table
3–19. Information is not available on
the safety of these vaccines when they are used during pregnancy;
it is prudent on theoretical grounds to avoid vaccinating pregnant
women. Live, attenuated Ty21a vaccine should not be given to immunocompromised
travelers, including those infected with human immunodeficiency virus
(HIV). The intramuscular vaccine presents theoretically safer alternatives
for this group. The only contraindication to vaccination with ViCPS
vaccine is a history of severe local or systemic reactions following
a previous dose. Neither of the available vaccines should be given
to travelers with an acute febrile illness.
Table 3–18.
Dosage and schedule for typhoid fever vaccination
Primary series |
6 years or older |
1 capsule*/oral |
4 |
48 hours |
Not applicable |
Booster |
6 years or older |
1 capsule*/oral |
4 |
48 hours |
Every 5 years |
Primary series |
2 years or older |
0.50 mL/
intramuscular |
1 |
Not applicable |
Not applicable |
Booster |
2 years or older |
0.50 mL/
intramuscular |
1 |
Not applicable |
Every 2 years |
|
|
Table 3–19.
Common adverse reactions to typhoid fever vaccines
|
Fever |
Headache |
Local Reactions |
Ty21a* |
0%–5% |
0%–5% |
Not applicable |
Vi Capsular polysaccharide |
0%–1% |
16%–20% |
7% erythema or induration 1 cm or smaller |
|
|
Precautions and Contraindications
Theoretical concerns have been raised about the
immunogenicity of live, attenuated Ty21a vaccine in persons concurrently
receiving antibiotics, immune globulin, or viral vaccines. The growth
of the live Ty21a strain is inhibited in vitro by various antibacterial
agents. Vaccination with Ty21a should be delayed for >24 hours
after the administration of any antibacterial agent. Available data
do not suggest that simultaneous administration of oral polio or
yellow fever vaccine decreases the immunogenicity of Ty21a. If typhoid
vaccination is warranted, it should not be delayed because of administration
of viral vaccines. Simultaneous administration of Ty21a and immune
globulin does not appear to pose a problem.
Other
See Risks
From Food and Drink.
— Steve
Luby, Eric Mintz, Padmini Srikantiah
|