Chapter 3Infectious Diseases Related To Travel
Typhoid & Paratyphoid Fever
Achuyt Bhattarai, Eric Mintz
Typhoid fever is an acute, life-threatening febrile illness caused by the bacterium Salmonella enterica serotype Typhi. Paratyphoid fever is a similar illness caused by S. Paratyphi A, B, or C.
MODE OF TRANSMISSION
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 rarely been documented.
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. Approximately 300 cases of typhoid fever and 150 cases of paratyphoid fever are reported each year in the United States, most of which are in recent travelers. The risk of typhoid fever is highest for travelers to southern Asia (6–30 times higher than for all other destinations). Other areas of risk include East and Southeast Asia, Africa, the Caribbean, and Central and South America. The risk of paratyphoid fever is also increasing among travelers to southern and Southeast Asia.
Travelers to southern Asia are at highest risk for infections that are nalidixic acid–resistant or multidrug-resistant (resistant to ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole). Travelers who are visiting friends and relatives (VFRs) are at increased risk (see Chapter 8, Immigrants Returning Home to Visit Friends and Relatives). Although the risk of acquiring typhoid or paratyphoid fever increases with the duration of stay, travelers have acquired typhoid fever even during visits <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. 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. 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 very low-grade septicemia. A single blood culture is positive in only half the cases. Stool culture is not usually positive during the acute phase of the disease. Bone marrow culture increases the diagnostic yield to about 80% of cases.
The Widal test is an old serologic assay for detecting IgM and IgG to the O and H antigens of salmonella. The test is unreliable but is widely used in developing countries because of its low cost. Newer serologic assays are somewhat more sensitive and specific than the Widal test but are infrequently available.
Because there is no definitive serologic test for typhoid or paratyphoid fever, the 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. Empiric treatment in most parts of the world would use a fluoroquinolone, most often ciprofloxacin. However, resistance to fluoroquinolones is highest in the Indian subcontinent and increasing in other areas. Injectable third-generation cephalosporins are often the empiric drug of choice when the possibility of fluoroquinolone resistance is high.
Patients treated with an appropriate antibiotic may still require 3–5 days to defervesce completely, although the height of the fever decreases each day. Patients may actually feel worse when the fever starts to go away. If fever does not subside within 5 days, alternative antimicrobial agents or other foci of infection should be considered.
PREVENTIVE MEASURES FOR TRAVELERS
Indications for Use
CDC recommends typhoid vaccine for travelers to areas where there is an increased risk of exposure to S.Typhi. The typhoid vaccines do not protect against S. Paratyphi infection. 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. Two typhoid vaccines are available in the United States:
- Oral live, attenuated vaccine (Vivotif vaccine, manufactured from the Ty21a strain of S. Typhi by Crucell/Berna)
- Vi capsular polysaccharide vaccine (ViCPS) (Typhim Vi, manufactured by Sanofi Pasteur) for intramuscular use
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%). 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 this group. The only contraindication to vaccination with ViCPS vaccine is a history of severe local or systemic reactions after a previous dose. Neither of the available vaccines should be given to people with an acute febrile illness.
Precautions and Contraindications
Theoretical concerns have been raised about the immunogenicity of live, attenuated Ty21a vaccine in people concurrently receiving antimicrobials (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. Dosage and schedule for typhoid fever vaccination
|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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- Gupta SK, Medalla F, Omondi MW, Whichard JM, Fields PI, Gerner-Smidt P, et al. Laboratory-based surveillance of paratyphoid fever in the United States: travel and antimicrobial resistance. Clin Infect Dis. 2008 Jun 1;46(11):1656–63.
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- Simanjuntak CH, Paleologo FP, Punjabi NH, Darmowigoto R, Soeprawoto, Totosudirjo H, et al. Oral immunisation against typhoid fever in Indonesia with Ty21a vaccine. Lancet. 1991 Oct 26;338(8774):1055–9.
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