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.

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