While tomatoes were identified early as an outbreak vehicle, subsequent investigation revealed Serrano and jalapeno peppers as the common food item in later outbreaks. I agree with Dr. Acheson that the epidemiological association is only an approximation and there will be a potential for things to occur by chance alone and confounders, but the relationships here are difficult to dismiss without some kind of explanation.
The short list includes cross contamination during repacking, common growing or harvesting methods, in common contaminated water supplies and irrigation, maybe even run-off.
We really do not know exactly what went wrong at the various production stages with these commodities and there is something important to learn from this either way.
2008 Outbreak of Salmonella Saintpaul infections associated with raw produce
New England Journal of Medicine
Casey Barton Behravesh, D.V.M., Dr.P.H., Rajal K. Mody, M.D., M.P.H., Jessica Jungk, M.P.H., Linda Gaul, Ph.D., M.P.H., John T. Redd, M.D., M.P.H., Sanny Chen, Ph.D., M.H.S., Shaun Cosgrove, B.A., Erin Hedican, M.P.H., David Sweat, M.P.H., Lina Chávez-Hauser, M.A., Sandra L. Snow, M.D., Heather Hanson, M.P.H., Thai-An Nguyen, M.P.H., Samir V. Sodha, M.D., M.P.H., Amy L. Boore, Ph.D., M.P.H., Elizabeth Russo, M.D., Matthew Mikoleit, M.A.S.C.P., Lisa Theobald, B.S., Peter Gerner-Smidt, M.D., D.M.S., Robert M. Hoekstra, Ph.D., Frederick J. Angulo, D.V.M., Ph.D., David L. Swerdlow, M.D., Robert V. Tauxe, M.D., M.P.H., Patricia M. Griffin, M.D., and Ian T. Williams, Ph.D. for the Salmonella Saintpaul Outbreak Investigation Team
Raw produce is an increasingly recognized vehicle for salmonellosis. We investigated a nationwide outbreak that occurred in the United States in 2008.
We defined a case as diarrhea in a person with laboratory-confirmed infection with the outbreak strain of Salmonella enterica serotype Saintpaul. Epidemiologic, traceback, and environmental studies were conducted.
Among the 1500 case subjects, 21% were hospitalized, and 2 died. In three case–control studies of cases not linked to restaurant clusters, illness was significantly associated with eating raw tomatoes (matched odds ratio, 5.6; 95% confidence interval [CI], 1.6 to 30.3); eating at a Mexican-style restaurant (matched odds ratio, 4.6; 95% CI, 2.1 to ∞) and eating pico de gallo salsa (matched odds ratio, 4.0; 95% CI, 1.5 to 17.8), corn tortillas (matched odds ratio, 2.3; 95% CI, 1.2 to 5.0), or salsa (matched odds ratio, 2.1; 95% CI, 1.1 to 3.9); and having a raw jalapeño pepper in the household (matched odds ratio, 2.9; 95% CI, 1.2 to 7.6). In nine analyses of clusters associated with restaurants or events, jalapeño peppers were implicated in all three clusters with implicated ingredients, and jalapeño or serrano peppers were an ingredient in an implicated item in the other three clusters. Raw tomatoes were an ingredient in an implicated item in three clusters. The outbreak strain was identified in jalapeño peppers collected in Texas and in agricultural water and serrano peppers on a Mexican farm. Tomato tracebacks did not converge on a source.
Although an epidemiologic association with raw tomatoes was identified early in this investigation, subsequent epidemiologic and microbiologic evidence implicated jalapeño and serrano peppers. This outbreak highlights the importance of preventing raw-produce contamination.