Impact of infecting dose on severity of disease in an outbreak of food-borne Salmonella enteritidis

We conducted a cross-sectional study 72 h after a private dinner party, at which 33/59 participants (attack rate 56%) became infected with Salmonella enteritidis, phage type 6. All were interviewed and stool samples were obtained from 55 persons (93%). Only 2/33 cases were asymptomatic (6%). The median incubation period was 21 h. 14 of the cases (42%) were admitted to hospital. A significant association was found between infection and 1 of the egg-containing dishes (kabab). Cross-contamination to other dishes was likely. As an indirect measure of infecting dose, all persons were divided into exposure groups according to self-reported amount of consumed kabab, which was associated with risk of becoming ill (p = 0.00002) and the risk of hospitalization (p = 0.0005). Among the symptoms experienced by the patients, only fever was significantly associated with the amount of consumed kabab (p = 0.008). The present data suggest an existence of a dose-effect relationship in infections with S. enteritidis, phage type 6.