S. typhi and S. paratyphi are transmitted in food or water contaminated by the faeces or urine of infected individuals.
In westernised countries this often results from inadvertent contamination of food during preparation by a patient or an unrecognised carrier, sometimes a migrant from an endemic area. A person may remain a chronic carrier for many years.
In less developed countries, transmission may be via uncooked and unwashed fruit and vegetables which have been grown in fields fertilized by human excreta, or shellfish harvested in sewage-polluted water.
Last reviewed 01/2018