The typhoid bacillus Salmonella typhi, which infects humans only. Paratyphoid and enteric fevers are caused by other species of Salmonella, which infect domestic animals as well as humans.
The typhoid bacillus 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; transmission also occurs through eating raw fruit and vegetables fertilized by human excreta 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
Typhoid fever is 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, some patients develop sustained fever, bradycardia, hepatosplenomegaly, abdominal symptoms and, occasionally, 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 cerebral complications, which may prove fatal in up to 10–20% of cases. The highest casefatality rates are reported in children <4 years of age. 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.
For general precautions against exposure to foodborne and waterborne infections, see Chapter 3.