Risk factors for sporadic infection with Salmonella Enteritidis, Denmark, 1997-1999

In a prospective case-control study of sporadic Salmonella Enteritidis infection in Denmark (1997-1999), foreign travel was reported by 25% of 455 case patients and 8% of 507 controls (odds ratio (OR) = 3.7, 95% confidence interval (CI): 2.4, 5.5). Among nontravelers, 80% of 335 cases and 81% of 467 controls had consumed eggs or dishes containing raw or undercooked eggs during the week before disease onset or interview, while 35% of cases and 19% of controls had incurred this exposure the day before onset or interview (OR = 2.2, 95% CI: 1.5, 3.1). Specific exposures included consumption of buttermilk dessert (OR = 11.7), homemade ice cream (OR = 4.3), raw eggs (OR = 3.4), and eggs fried sunny side up (OR = 2.5). Among persons who had used eggs in the week before disease onset or interview, eggs from battery laying hens were associated with disease (white eggs: OR = 2.4, brown eggs: OR = 1.9), whereas consumption of pasteurized eggs tended to be protective (OR = 0.3). The study confirmed that eggs are the principal source of S. Enteritidis in Denmark. This conclusion was reached through the use of an exposure time window that corresponds to the most relevant incubation period rather than the maximum incubation period. The authors recommend this method in studies that have the objective of determining risk associated with common exposures.