Causative agents
Typhoid and paratyphoid fevers are caused by the bacteria Salmonella Typhi and Salmonella Paratyphi respectively.

Clinical features
Symptoms of typhoid fever include sustained fever, malaise, poor appetite, severe headache and vomiting. In adults, constipation is a more common symptom than diarrhoea. Enlarged spleen and liver, and rose-coloured spots on the chest are sometimes noted. It can be complicated by intestinal bleeding and perforation, impaired consciousness and even death if untreated. Occasionally, infected individuals may be asymptomatic but able to shed bacteria in their faeces or urine. Paratyphoid fever presents with similar picture, but tends to be milder.

Mode of transmission
Typhoid and paratyphoid fevers are transmitted via faecal-oral route. The causative bacteria are passed in the faeces and urine of infected people, which may contaminate food, water or beverages and cause infection in the consumer of such contaminated food. Types of food which are susceptible to contamination include shellfish (particularly oysters), raw fruits and vegetables and unpasteurised milk and dairy products.

Incubation period
Incubation period is 7-21 days.