Fresh herbs and bagged salads can pose food safety risks

While the Canadian Food Inspection Agency was playing statistical silliness and gushing that 98 per cent of fresh leafy herbs sampled in 2009/2010 were not contaminated with bacterial pathogens or generic E. coli, researchers in Tennessee and the U.S. Centers for Disease Control published a more rigorous analysis of a multistate outbreak of Escherichia coli O157:H7 associated with bagged salad.

lettuce-skullI know; salad is not herbs. But they both have the potential to be contaminated.

Shiga toxin–producing Escherichia coli O157:H7 (STEC O157) is the most commonly identified serotype of STEC in the United States. An estimated 63,000 STEC O157 infections occur annually. Infection typically results in diarrhea, bloody stool, abdominal cramps, and, in some cases, hemolytic uremic syndrome. Recent outbreaks of STEC O157 have increasingly been associated with consumption of leafy greens such as lettuce and spinach. We investigated an outbreak of STEC O157 associated with the consumption of bagged salad with cases clustered in various institutional settings. A case–control study was conducted among cases from selected schools with controls matched by school and grade. Seventeen cases from three U.S. states were identified. The median age of cases was 23 years (range: 3–88) and 13 (76%) were female. Six cases were hospitalized and two died. Onset dates ranged from April 29 to May 12, 2012.

The matched case–control analysis identified a single significant food service exposure: consumption of lettuce provided by a school cafeteria (median odds ratio=9.4, 95% confidence interval: 1.4–∞, p=0.0469). The implicated bagged salad product was traced back to a single production facility. Implicated growing areas were scheduled for heightened inspection for the upcoming growing season. A combination of analytical epidemiologic studies among subclusters of cases, surveillance, and traceback implicated bagged salad in this outbreak investigation.

Foodborne Pathogens and Disease

Marder Ellyn P., Garman Katie N., Ingram Lily Amanda, and Dunn John R.

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About Douglas Powell

A former professor of food safety and the publisher of, Powell is passionate about food, has five daughters, and is an OK goaltender in pickup hockey. Download Doug’s CV here. Dr. Douglas Powell editor, retired professor, food safety 3/289 Annerley Rd Annerley, Queensland 4103 61478222221 I am based in Brisbane, Australia, 15 hours ahead of Eastern Standard Time