Chapter 3 Infectious Diseases Related to Travel
Typhoid & Paratyphoid Fever
Anna E. Newton, Janell A. Routh, Barbara E. Mahon
Typhoid fever is a potentially severe and occasionally life-threatening febrile illness caused by the bacterium Salmonella enterica serotype Typhi. Paratyphoid fever is a similar illness caused by S. enterica serotype Paratyphi A, B (tartrate negative), or C.
Humans are the only source of these bacteria; no animal or environmental reservoirs have been identified. Typhoid and paratyphoid fever are most often acquired through consumption of water or food that has been contaminated by feces of an acutely infected or convalescent person or a chronic, asymptomatic carrier. Transmission through sexual contact, especially among men who have sex with men, has been documented rarely.
An estimated 22 million cases of typhoid fever and 200,000 related deaths occur worldwide each year; an additional 6 million cases of paratyphoid fever are estimated to occur annually. Each year in the United States, approximately 300 culture-confirmed cases of typhoid fever and 100 cases of paratyphoid fever are reported. More than 80% of reports of typhoid fever and >90% of reports of paratyphoid fever caused by Salmonella Paratyphi A are of travelers to southern Asia. Other areas of risk include East and Southeast Asia, Africa, the Caribbean, and Central and South America. In certain regions, the risk of typhoid fever has decreased. As a result, CDC removed pre-travel typhoid vaccination recommendations for 26 countries in Eastern Europe and the Middle East; the most recent pre-travel vaccination guidelines can be found at www.cdc.gov/travel.
Travelers who are visiting friends and relatives are at increased risk (see Chapter 8, Immigrants Returning Home to Visit Friends & Relatives (VFRs)). Although the risk of acquiring typhoid or paratyphoid fever increases with the duration of stay, travelers have acquired typhoid fever even during visits of <1 week to countries where the disease is endemic.
The incubation period of typhoid and paratyphoid infections is 6–30 days. The onset of illness is insidious, with gradually increasing fatigue and a fever that increases daily from low-grade to as high as 102°F–104°F (38°C–40°C) by the third to fourth day of illness. Headache, malaise, and anorexia are nearly universal and abdominal pain, diarrhea, or constipation are common. Hepatosplenomegaly can often be detected. A transient, macular rash of rose-colored spots can occasionally be seen on the trunk. Fever is commonly lowest in the morning, reaching a peak in late afternoon or evening. This clinical presentation is often confused with malaria, and typhoid fever should be suspected in a person with a history of travel to an endemic area who is not responding to antimalarial medication. Untreated, the disease can last for a month. The serious complications of typhoid fever generally occur after 2–3 weeks of illness and may include intestinal hemorrhage or perforation, which can be life threatening.
Infection with typhoid or paratyphoid fever results in a low-grade septicemia. Although blood culture is the mainstay of diagnosis in typhoid fever, a single culture is positive in only approximately 50% of cases. Multiple cultures increase the sensitivity and may be required to make the diagnosis. Bone marrow culture increases the diagnostic yield to approximately 80% of cases. Stool culture is not usually positive during the earliest phase of the disease.
The Widal test is unreliable but is widely used in developing countries because of its low cost. It is a serologic assay for IgM and IgG to the O and H antigens of Salmonella Typhi, but is not specific and false positives may occur. Acute- and convalescent-phase titers are more sensitive than a single serum sample. Newer serologic assays for Salmonella Typhi infection are occasionally used in outbreak situations, and are somewhat more sensitive and specific than the Widal test, but are not an adequate substitute for blood, stool, or bone marrow culture.
Because there is no definitive serologic test for typhoid or paratyphoid fever, the initial diagnosis often has to be made clinically. The combination of a history of risk for infection and a gradual onset of fever that increases in severity over several days should raise suspicion of typhoid or paratyphoid fever.
Specific antimicrobial therapy shortens the clinical course of typhoid fever and reduces the risk for death. A fluoroquinolone, most often ciprofloxacin, is used for empiric treatment in most parts of the world. However, fluoroquinolone-resistant or multidrug-resistant (resistant to ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole) strains are common in the Indian subcontinent and increasing in other areas, such as Africa. Injectable third-generation cephalosporins are often the empiric drug of choice when the possibility of fluoroquinolone resistance is high. Azithromycin is increasingly used to treat typhoid fever or paratyphoid fever because of the emergence of multidrug-resistant strains, although increasing resistance to azithromycin in Salmonella Typhi strains has already been documented.
Patients treated with an antibiotic may remain febrile for 3–5 days, although the height of the fever generally decreases each day. Patients may actually feel worse during the several days it takes for the fever to end. If fever in a person with culture-confirmed typhoid or paratyphoid fever does not subside within 5 days, alternative antimicrobial agents or other foci of infection should be considered.
Food and Water
Safe food and water precautions and frequent handwashing are important in preventing typhoid and paratyphoid fever (see Chapter 2, Food & Water Precautions). Although vaccines are recommended to prevent typhoid fever, they are not 100% effective; therefore, even vaccinated travelers should follow recommended food and water precautions. For paratyphoid fever, these precautions are the only prevention method, as no vaccines are available.
Indications for Use
CDC recommends typhoid vaccine for travelers to areas where there is an increased risk of exposure to Salmonella Typhi. Two typhoid vaccines are available in the United States:
- Oral live attenuated vaccine (Vivotif, manufactured from the Ty21a strain of Salmonella Typhi by PaxVax)
- Vi capsular polysaccharide vaccine (ViCPS) (Typhim Vi, manufactured by Sanofi Pasteur) for intramuscular use
Both typhoid vaccines protect 50%–80% of recipients; travelers should be reminded that typhoid immunization is not 100% effective, and typhoid fever could still occur. Available typhoid vaccines offer limited or no protection against Salmonella Paratyphi infection.
Table 3-20 provides information on vaccine dosage, administration, and revaccination. The time required for primary vaccination differs for the 2 vaccines, as do the lower age limits.
Primary vaccination with oral Ty21a vaccine consists of 4 capsules, 1 taken every other day. The capsules should be kept refrigerated (not frozen), and all 4 doses must be taken to achieve maximum efficacy. Each capsule should be taken with cool liquid no warmer than 98.6°F (37°C), 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 aged <6 years.
Primary vaccination with ViCPS consists of one 0.5-mL (25-mg) dose administered intramuscularly. One dose of this vaccine should be given ≥2 weeks before expected exposure. The manufacturer does not recommend the vaccine for infants and children aged <2 years.
Vaccine Safety and Adverse Reactions
Adverse reactions to Ty21a vaccine are rare and mainly consist of abdominal discomfort, nausea, vomiting, and rash. ViCPS vaccine is most often associated with headache (16%–20%) and injection-site reactions (7%).
Precautions and Contraindications
No information is available on the safety of these vaccines in 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 HIV. The intramuscular vaccine presents a theoretically safer alternative for immunocompromised travelers. (The Advisory Committee on Immunization Practices does not recommend against vaccinating household contacts of immunocompromised people with Ty21a; although vaccine organisms can be shed transiently in the stool of vaccine recipients, secondary transmission of vaccine organisms has not been documented.) The only contraindication to vaccination with ViCPS vaccine is a history of severe local or systemic reactions after a previous dose. Neither vaccine should be given to people with an acute febrile illness.
Theoretical concerns have been raised about the immunogenicity of live, attenuated Ty21a vaccine in people concurrently receiving antimicrobial agents (including antimalarial chemoprophylaxis), viral vaccines, or immune globulin. The growth of the live Ty21a strain is inhibited in vitro by various antibacterial agents, and vaccination with Ty21a should be delayed for >72 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.
Table 3-20. Vaccines to prevent typhoid fever
|AGE (y)||DOSE, MODE OF ADMINISTRA-
|NUMBER OF DOSES||DOSING INTERVAL||BOOSTING INTERVAL|
|Oral, Live, Attenuated Ty21a Vaccine (Vivotif)1|
|Primary series||≥6||1 capsule,2 oral||4||48 hours||Not applicable|
|Booster||≥6||1 capsule,2 oral||4||48 hours||Every 5 years|
|Vi Capsular Polysaccharide Vaccine (Typhim Vi)|
|Primary series||≥2||0.50 mL, intramuscular||1||Not applicable||Not applicable|
|Booster||≥2||0.50 mL, intramuscular||1||Not applicable||Every 2 years|
1The vaccine must be kept refrigerated (35.6°F–46.4°F, 2° C–8°C).
2Administer with cool liquid no warmer than 98.6°F (37°C).
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