Incubation period and other features of food-borne and water-borne outbreaks of typhoid fever in relation to pathogenesis and genetics of resistance.

Examination of the incubation period of typhoid fever, the attack rate, and the spread of the case-onset pattern in food-borne and water-borne outbreaks and in experimental infections indicates that typhoid fever arises when organisms invade the circulation by at least two mechanisms--as a result of either the net growth of invading organisms at an early stage or a breakdown in host cellular mechanisms later. The distribution of case-onset patterns suggests that a small number of genes, possibly a single gene, controls host resistance in the early phase. The occurrence of bimodal or even trimodal case-onset patterns in a population exposed to infection by a particular dose of organisms reveals differences in genetic resistance within the population.