Risk factors for sporadic salmonellosis in Switzerland

A case-control study was conducted to identify determinants for the acquisition of sporadic Salmonella infection in Switzerland. Over a one-year period (1993), 223 case-control pairs were enrolled in the study and risk factors were assessed by means of self-administered questionnaires. Three-quarters of the isolates were identified as Salmonella enteritidis, most of which (80%) belonged to phage type 4. There were distinct differences in risk factors between infections with Salmonella enteritidis and those with other Salmonella serovars. In both groups recent travel abroad was positively associated with illness. This association was more pronounced for infections with non-enteritidis salmonellae [odds ratio (OR) 39.5; 95% confidence interval (CI) 6.6-236.8, compared to Salmonella enteritidis 4.0; 95% CI 1.8-9.1]. Among the presumably imported infections, Salmonella enteritidis was acquired mostly in other European countries, while other serovars were acquired mostly in countries outside of Europe. Eating food containing raw or undercooked eggs during the three days before the onset of illness increased the risk of infection with Salmonella enteritidis. Desserts made with raw eggs (OR 4.6; 95% CI 2.0-10.6) were more strongly associated with disease than consumption of soft-boiled eggs (OR 2.1; 95% CI 1.2-3.7), suggesting that the risk of infection was dependent on the extent to which eggs were cooked. Egg consumption was not associated with infections with serovars other than Salmonella enteritidis; however, the intake of medications other than antacids was found to be a risk factor (OR 3.5; 95% CI 1.1-11.4).