Salmonella typhi, the typhoid bacillus, which infects only humans. Paratyphoid and enteric fevers are caused by other species of Salmonella, which infect domestic animals as well as humans.
Infection is transmitted by consumption of contaminated food or water. Occasionally direct faecal–oral transmission may occur. Shellfish taken from sewage-polluted areas are an important source of infection. Infection occurs also through eating raw fruit and vegetables fertilized by night soil, and through ingestion of contaminated milk and milk products. Flies may cause human infection through transfer of the infectious agents to foods. 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, which fade on pressure, appear on the skin of the trunk in up to 20% of cases. In the third week, untreated cases may develop 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.
There is a higher risk of typhoid fever in countries or areas with low standards of hygiene and water supply facilities.
Risk for travellers
The risk for travellers is generally low, except in parts of northern and western Africa, in southern Asia, in parts of Indonesia and in Peru. Elsewhere, travellers are usually at risk only when exposed to low standards of hygiene. Even vaccinated travellers should take care to avoid consumption of potentially contaminated food and water as the vaccine does not confer 100% protection.
Observe all precautions against exposure to foodborne and waterborne infections (Chapter 3).