Routine Collection of Exposure Data from Sporadic Salmonellosis Cases - Foodborne Diseases Active Surveillance Network, 2014

BACKGROUND:  An estimated 1.2 million salmonellosis cases occur in the United States annually. Determining the proportion of Salmonella infections due to specific foods, settings, and nonfood exposures is essential to inform the development of effective regulations and interventions. Exposure data from salmonellosis cases are needed for attributing the sources of illnesses accurately and, in the past, have been gathered primarily from case-control studies, which are resource-intensive and not conducted regularly. To better understand sources of exposure and collect this information on a timelier basis, the Foodborne Disease Active Surveillance Network (FoodNet) began routine collection of standardized exposure data for salmonellosis cases.

METHODS:  FoodNet conducts active surveillance for culture-confirmed salmonellosis. In January 2014, FoodNet sites started collecting standardized exposure data, including food consumption, animal contact, and water exposures. We compared exposures betwen sporadic Salmonella Enteritidis (SE) cases and all other Salmonella serotypes using chi-square analysis, adjusting for site and season during which illness occurred, to identify differences in proportion of exposures reported.

RESULTS: During January to September 2014, there were 428 sporadic SE cases and 1,475 other Salmonella cases with exposure data reported. More SE cases reported consuming chicken (78% vs. 70%, p=0.004), chicken outside the home (42% vs. 35%, p=0.003), raw fish (7% vs. 3%, p=0.013), eggs (67% vs. 59%, p=0.008), eggs outside the home (19% vs. 12%, p=0.006), lettuce (57% vs. 44%, p=0.002), and spinach (23% vs. 16%, p=0.02) in the week before illness onset than other Salmonella cases. In contrast, fewer SE patients reported contact with reptiles and amphibians (7% vs. 9%, p=0.004), visiting a farm or ranch (3% vs. 8%, p<0.001), contact with ruminants (2% vs. 4%, p=0.02), having a septic system (22% vs. 34%, p<0.001), and drinking well water (12% vs. 19%, p=0.002) than other Salmonella cases.

CONCLUSIONS:  This case-case comparison showed that SE patients were more likely than other persons with salmonellosis to report food exposures, including chicken, eggs, raw fish, lettuce, and spinach, and less likely to report environmental exposures, including animal contact, visiting a farm or ranch, and drinking well water, when compared to other Salmonella cases. Routinely collecting standardized exposure data from sporadic cases might allow for more timely data analyses to inform source attribution estimates and interventions.