Cause
Salmonella typhi, the typhoid bacillus, which infects only humans. Similar paratyphoid and enteric fevers are caused by other species of Salmonella, which infect domestic animals as well as humans.
Transmission
Infection is transmitted by consumption of contaminated food or water. Occasionally direct faecal–oral transmission may occur. Shellfish taken from sewage-polluted beds are an important source of infection. Infection occurs through eating fruit and vegetables fertilized by night soil and eaten raw, and milk and milk products that have been contaminated by those in contact with them. Flies may transfer infection to foods, resulting in contamination that may be sufficient to cause human infection. Pollution of water sources may produce epidemics of typhoid fever, when large numbers of people use the same source of drinking-water.
Nature of the disease
A systemic disease of varying severity. Severe cases are characterized by gradual onset of fever, headache, malaise, anorexia and insomnia. Constipation is more common than diarrhoea in adults and older children. Without treatment, the disease progresses with sustained fever, bradycardia, hepatosplenomegaly, abdominal symptoms and, in some cases, pneumonia. In white-skinned patients, pink spots (papules), which fade on pressure, appear on the skin of the trunk in up to 50% of cases. In the third week, untreated cases develop additional gastrointestinal and other complications, which may prove fatal. Around 2–5% of those who contract typhoid fever become chronic carriers, as bacteria persist in the biliary tract after symptoms have resolved.
Geographical distribution
Worldwide. The disease occurs most commonly in association with poor standards of hygiene in food preparation and handling and where sanitary disposal of sewage is lacking.
Risk for travellers
All travellers to endemic areas are at potential risk of typhoid fever, although the risk is generally low in tourist and business centres where standards of accommodation, sanitation and food hygiene are high. The risk is particularly high in the Indian subcontinent. Even vaccinated individuals should take care to avoid consumption of potentially contaminated food and water as the vaccine does not confer 100% protection.
Vaccine
Travellers to countries where the risk of typhoid fever is high, where hygiene is poor, and where there is a high prevalence of antibiotic-resistant organisms, may be offered one of the following vaccines.
- Oral Ty21a. This live, attenuated mutant strain of Salmonella typhi Ty21a, supplied as enteric coated capsules, is given orally in three doses (four in North America) 2 days apart, and produces protection 7 days after the fi nal dose. Seven years after the fi nal dose the protective effi cacy is 67% in residents of endemic areas but may be less for travellers. A liquid formulation is no longer available.
- Injectable Vi CPS. Capsular Vi polysaccharide vaccine (Vi CPS), containing 25 µg of polysaccharide per dose, is given i.m. in a single dose and produces protection 7 days after injection. In endemic areas, the protective effi cacy after vaccination is 72% after 1.5 years and 50% after 3 years.
Both vaccines are safe and effective. However, their effi cacy in children under 2 years of age has not been demonstrated.
A combined typhoid/hepatitis A vaccine is also available in some countries.
Precautions and contraindications
Proguanil, mefl oquine and antibiotics should be stopped from 3 days before until 3 days after giving Ty21a.
No serious adverse effects have been reported following administration of Ty 21a or Vi CPS.
These vaccines are not recommended for use in infant immunization programmes:
there is insufficient information on their effi cacy in children under 2 years of age.
Type of vaccine: Oral Ty21a and injectable Vi CPS
Number of doses: One of Vi CPS, i.m. Three or four of live Ty21a, given orally at 2-day intervals as enteric coated capsule
Booster: Every 2 to 3 years for Vi CPS; for Ty21a see package inserta
Contraindications: Proguanil, mefloquine and antibiotics 3 days before or after starting Ty21a
Adverse reactions: None significant
Before departure: 1 week
Recommended for: Travellers to high-risk areas and travellers staying longer than 1 month or likely to consume food or beverages away from the usual tourist routes in developing countries
Special precautions: Vi CPS – not under 2 years of age; avoid proguanil, mefloquine and antibiotics with Ty21a