Miami Beach, Florida, Collins Avenue, Publix, supermarket, prepackaged lettuce arugula spinach, organic produce retail, plastic containers on shelf, Organic Girl Greenwise Taylor Farms, customer selecting. (Photo by: Jeffrey Greenberg/Universal Images Group via Getty Images)
Jeffrey Greenberg/Universal Images Group via Getty Images
The FDA retracted the results of a single lab test in the ongoing cyclospora outbreak linked to Taco Bell lettuce. Now there is growing public confusion about what to believe. I served as an Epidemic Intelligence Service Officer for the CDC and I understand how outbreak investigations work. Hearing that a single lab test did not confirm the presence of the parasite might be confusing but one data point, like a negative test or a retraction, does not automatically mean public health investigators have it wrong.
There is a rigorous, time-tested approach for identifying culprits in food outbreaks. For decades, this approach has solved outbreak after outbreak. These include notable ones like the 1993 Jack in the Box E. coli outbreak traced to undercooked hamburger patties, the 2006 spinach E. coli outbreak traced to a California growing region, the 2011 Jensen Farms cantaloupe listeria outbreak and the 2018 romaine lettuce E. coli outbreak traced to Yuma, Arizona.
Identifying the source of a foodborne outbreak requires laboratory testing, but the source is most often first identified through context, stories and recall from the people affected. Investigators interview far more people than may actually be sick; we call this “casting a wide net,” asking about time, place, and exposure, in this case to specific foods. When the data are compiled and reviewed, investigators look for what the sick people have in common. Sifting through and figuring out which information is relevant can be tedious and time-consuming.
This incident with FDA lab testing reminds me of an investigation I conducted in Indiana. There, a mismatch existed between the lab results and the information gathered by the health department. The source was a mystery. Finding it wasn’t a breakthrough from DNA genotyping. The answer came from time and attention, building enough trust to listen to people’s stories and experiences until the chain of transmission became clear.
Outbreak investigations require both quantitative and qualitative data: crunching numbers and gathering context from the people affected and involved. If one piece is later found to be flawed, that doesn’t erase the value of the other.
But outbreak investigation is not flawless. Public health field investigations take time and can be a series of hits and misses, dead ends explored, clues misread, wrong paths followed before landing on the right one. Identifying which item at Taco Bell is transmitting cyclospora is the challenge. In this outbreak, Michigan health officials interviewed 190 people who had eaten at Taco Bell and gotten sick; 90% of them reported eating iceberg lettuce. That is a solid, credible finding independent of a single lab result.
Foodborne outbreaks can be challenging to solve. Successfully identifying the source requires time, patience, teamwork and transparency. This case will be solved. Our duty as the public is to have patience too, and to trust a scientific process that has proven itself again and again. Let the experts do the work they’re trained to do. We should soon have the answer.