Summertime Blues: lowering bacterial loads from farm-to-fork means fewer sick people

Every summer, government agencies at the local state and federal level in Western countries around the world warn consumers to be extra super-duper careful when barbecuing, because the incidence of foodborne illness, especially E. coli O157:H7, goes up in the warm summer months, and this is because consumers are doing dumb things at the grill.

I never believed it – consumers, food service workers, humans are capable of doing dumb things wherever they are cooking – but it was another standard line in the blame-the-consumer approach to food safety risk reduction.

There has been plenty of evidence over the years to show that the increase in human illnesses in summer months is strongly correlated to overall increases in E. coli O157:H7 loads in cattle in summer months.

Lower the loads, reduce the risk.

Most food safety interventions are designed to reduce or eliminate pathogen loads – to lower the number of harmful bugs from farm-to-fork. A piece of highly-contaminated meat can wreck cross-contamination havoc in a food service or home kitchen.

A new paper in Foodborne Pathogens and Disease by researchers from the U.S. Department of Agriculture and the University of Nebraska-Lincoln uses models representing seasonal variation in E. coli O157:H7 loads in the farm-to-fork continuum, and concludes that summertime cooking is as risky as the rest of the year.

The authors write:

“A plausible explanation for the increase in E. coli O157:H7 illness during the summer is poor consumer storage and cooking practices associated with meals prepared and cooked outdoors (e.g., picnics and barbeques). If these practices are major contributors to human illness, then an effective mitigation strategy could be additional labeling and consumer education regarding the need to maintain meat products at temperatures sufficiently low to avoid bacterial growth during transportation to outdoor venues and to cook products to a sufficient temperature when grilling. Conversely, if summer storage and cooking practices are not responsible for a large proportion of summer illnesses, a more effective mitigation strategy would reduce the seasonal effect of E. coli O157:H7 contamination at the preharvest stage or during the production and processing of beef. …

“The seasonal change in the probability of exposure to a contaminated serving is the primary driver of the season pattern in illnesses, rather than any seasonal changes in consumer storage and handling.”

The complete abstract is below.

Determining relationships between the seasonal occurrence of Escherichia coli O157:H7 in live cattle, ground beef, and humans
Foodborne Pathogens and Disease. October 2010, 7(10): 1247-1254
Michael S. Williams, James L. Withee, Eric D. Ebel, Nathan E. Bauer, Wayne D. Schlosser, William T. Disney, David R. Smith, Rodney A. Moxley
The prevalence and concentration of many foodborne pathogens exhibit seasonal patterns at different stages of the farm-to-table continuum. Escherichia coli O157:H7 is one such pathogen. While numerous studies have described the seasonal trend of E. coli O157:H7 in live cattle, ground beef, and human cases, it is difficult to relate the results from these different studies and determine the interrelationships that drive the seasonal pattern of beef-related human illnesses. This study uses a common modeling approach, which facilitates the comparisons across data sets, to relate prevalence in live cattle to raw ground beef and human illness. The results support an intuitive model where a seasonal rise of E. coli O157:H7 in cattle drives increased ground beef prevalence and a corresponding rise in the human case rate. We also demonstrate the use of these models to assess the public health impact of consumer behaviors. We present an example that suggests that the probability of illness, associated with summertime cooking and handling practices, is not substantially higher than the baseline probability associated with more conventional cooking and handling practices during the remainder of the year.