Typhoid Fever

Description

Typhoid fever is an acute, life-threatening febrile illness caused by the bacterium Salmonella typhi. The disease is characterized by fever, headache, malaise, anorexia, splenomegaly, and a relative bradycardia. Many mild and atypical infections occur.

Occurrence

As estimated 16 million cases of typhoid fever and 600,000 related deaths occur worldwide. An estimated 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 from 1992 through 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 to other developing 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.

Preventive Measures

Vaccine

Two typhoid vaccines are currently available for use in the United States: (1) an oral, live, attenuated vaccine (Vivotif Berna™ vaccine, manufactured from the Ty21a strain of S. typhi by the Swiss Serum and Vaccine Institute) and (2) a Vi capsular polysaccharide vaccine (ViCPS) (Typhim Vi, manu-factured by Aventis Pasteur) for parenteral use. Both vaccines have been shown to protect 50% to 80% of recipients. The parenteral heat-phenol-inactivated vaccine (manufactured by Wyeth-Ayerst) has been discontinued.

Table 3-16 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 among 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° Celsius (98.6° Fahrenheit), approximately one hour before a meal. The vaccine manufacturer recommends that Ty21a not be administered to infants or children younger than 6 years of age. Primary vaccination with ViCPS consists of one 0.5-milliliter (mL) (25-microgram) dose administered intramuscularly. The manufacturer does not recommend the vaccine for infants younger than 2 years of age. (See Chapter 1, "Vaccination Information," "Vaccine Recommendations for Infants and Children," "Typhoid Vaccine," page 18, for a discussion of typhoid immunization for infants who will be traveling.) Current recommendations for revaccination are provided in Table 3-16.

Adverse Reactions

Information on adverse reactions is presented in Table 3-17. 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 parenteral 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 3-16.--Dosage and Schedule for Typhoid Fever Vaccination. ORAL, LIVE, ATTENUATED TY21A VACCINE

Vaccination Age Dose/Mode of
Administration Number
of Doses Dosing
Interval Boosting
Interval
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
VI CAPSULAR POLYSACCHARIDE VACCINE
Vaccination Age Dose/Mode of
Administration Number
of Doses Dosing
Interval Boosting
Interval
Primary series 2 years or older 0.50 milliliters/
Intramuscular 1 Not applicable Not applicable
Booster 2 years or older 0.50 milliliters/
Intramuscular 1 Not applicable Every 2
years
* Administer with cool liquid no warmer than 37° C (98.6° F).

Table 3-17.--Common Adverse Reactions to Typhoid Fever Vaccines. Vaccine Reactions
Fever Headache Local Reactions
Ty21a* 0%-5% 0%-5% Not Applicable
Vi Capsular
Polysaccharide 0%-1% 1.5%-3% 7% Erythema or Induration < 1 cm
* The side effects of Ty21a are rare and mainly consist of abdominal discomfort, nausea, vomiting, and rash or urticaria.

Precautions and Contraindications

Theoretical concerns have been raised regarding the immunogenicity of live, attenuated Ty21a vaccine in people concurrently receiving antibiotics, immune globulin, antimalarials, or viral vaccines. The growth of the live Ty21a strain is inhibited in vitro by various antibacterial agents and by the antimalarial prophylactic agent mefloquine. Simultaneous administration of the antimalarial prophylactic agent proguanil with Ty21a vaccine resulted in significantly lower combined IgG or IgA anti-S. typhi lipopolysaccharide antibody response. The anti-S. typhi lipopolysaccharide antibody response was not significantly decreased when mefloquine was administered concurrently with Ty21a. Vaccination with Ty21a should not be administered concurrently with proguanil prophylaxis and should be delayed for more than 24 hours after the administration of any antibacterial agent or mefloquine. Chloroquine does not significantly inhibit the growth of Ty21a or the anti-S. typhi antibody response, and can be given concurrently. 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 the administration of viral vaccines. Simultaneous administration of Ty21a and immune globulin does not appear to pose a problem.

Credits: National Center of Infectious Diseases