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In search of the source: the latest cyclospora outbreak

USA cyclospora map courtesy CDC

Cyclospora has captured national headlines this summer; attention prompted in part by public health experts who have questioned the methodology used to identify the culprit behind our country’s latest outbreak of foodborne illness.

When outbreaks of infection credited to cyclospora originally occurred in Iowa and Nebraska, public health officials attributed the infections to contaminated salad mixes packaged by Taylor Farms de Mexico. When that company stopped producing and shipping the product in early August, many assumed the infections would stop shortly afterward.

Yet two weeks later the number of documented infections has continued to climb.

According to the US Centers for Disease Control and Prevention (CDC), over 600 people in 22 states have now been impacted by the intestinal infection, nearly 75 of which were confirmed after Taylor Farms de Mexico made moves to end consumer exposure to their salad mix.

Even with a 1-2 week long incubation period, some public health experts have started to wonder aloud whether the original source was entirely accurate. Others have questioned the lack of information about how Iowa and Nebraska arrived at their conclusion.

“The challenge with foodborne illness outbreaks that involve several states, is that local health departments act somewhat independently so there isn’t one designated department directing how the investigation should be conducted,” said Craig Hedberg, Ph.D., a University of Minnesota School of Public Health epidemiologist and food safety expert who has nearly 20 years of experience in tracing foodborne illness and infectious disease outbreaks. “As a result, there isn’t the level of coordination that can sometimes yield a swift and thorough answer to a given foodborne illness.”

According to Hedberg, who isn’t directly involved in the current cyclospora investigation, there were an unusual number of cases of cyclospora reported initially, prompting patient interviews so experts could determine potential commonality. Once 80 percent of infected consumers confirmed they ate salad at Red Lobster or Olive Garden – both of which used the Taylor Farms product – the salad mix was identified as the source.

The problem with that conclusion is that the bagged salad may not tell the whole story.

Hedberg said that in Minnesota, epidemiologists conduct detailed exposure assessments and epidemiologic studies to trace the source through a proven system coined the Minnesota Model for Food Safety. The model was developed in collaboration between the Minnesota Department of Health and the University of Minnesota and has been cited as a national model for investigating foodborne illness and disease outbreaks.

The Minnesota Model for Food Safety employs the following tactics:

1)   A patient visits a physician complaining of food poisoning and has a stool sample collected to identify the cause (E Coli, Salmonella, Cyclospora, etc).
2)   Patients are questioned to identify food items eaten, and the source of those food items, during the period when they would have acquired their illness.
3)   When several possibly related cases come in, an investigation is launched to find a common source of exposure.
4)   When a common restaurant is identified, dining partners who aren’t sick are also questioned to eliminate food that might otherwise be a suspect.
5)   Recipes are cross-examined for overlapping ingredients.
6)   Suspected food items or ingredients are traced back to their point of origin.

“We have to examine every possible outcome to pinpoint the source,” said Hedberg. “Two infected patrons may have eaten different items and if both were asked whether or not they ate parsley, they might have different answers. But if they’re both shown the menu and tell us what they ate, it may turn out that both of their meals contained parsley. At that point we could consider parsley a potential source.”

Although cyclospora is not considered fatal, most people who are infected battle intestinal issues that can last for days. Most healthy people can fight off the infection easily, but without medical intervention some cases can linger for weeks.

Stay tuned to Health Talk for future updates around cyclospora and other foodborne illness outbreaks.


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