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A US outbreak of a serious gastrointestinal illness caused by a food-borne parasite has continued to grow by hundreds of cases per day as authorities struggle to identify the source.
Michigan, the centre of the outbreak, reported over 400 new cases of cyclosporiasis on Tuesday for a total of 6,571 since June 21, skyrocketing above the state average of 50 cases per year. Other states in the Midwest and Northeast have also reported hundreds of cases apiece.
Michigan’s state health department first publicly identified an uptick in cyclosporiasis on July 1. As cases mounted, initial investigative efforts pointed to lettuce provided by grower Taylor Farms to Taco Bell restaurants.
The Mexican-themed fast-food chain voluntarily pulled Taylor Farms lettuce from its menus nationwide on Friday. Foot traffic at Taco Bell dropped nearly 31 per cent on Friday compared to the day-of-the-week average this year, according to market researcher Placer.ai.
However, the Food and Drug Administration on Sunday walked back test results identifying the cyclospora parasite on lettuce from Taylor Farms, saying the result was a “false positive”.
Epidemiological efforts to trace the pathogen still show a “strong signal” towards lettuce or salad greens as a source of the outbreak, according to the Michigan state health department.
The state has also seen cases where patients “report neither consuming lettuce nor eating at any particular fast-food chain”, said Natasha Bagdasarian, chief medical executive for the state of Michigan. “It is possible, with the types of numbers that we are seeing, that there are two separate things happening,” she said.
Taylor Farms is continuing with its recall of iceberg lettuce despite the FDA test retraction. The brand recalled lettuce grown in central Mexico and will not source from the region for the rest of the growing season, it said in a statement.
Neither Taylor Farms nor Taco Bell responded to a request for comment.
Cyclospora is very difficult to identify in lab tests, said Karen Levy, a professor researching foodborne illnesses at the University of Washington. “There’s a lot of potential for false positives,” she said.
In general, it is “not unusual” for an outbreak investigation to identify a contamination source entirely by interviewing patients, without ever obtaining a definitive test result, said Jodie Guest, senior vice-chair of epidemiology at Emory University.
Michigan and other states are tracing the outbreak via interviews with patients, which take about 45 minutes each and require patients to recall to health officials everything they’ve eaten in a two-week period.
Bagdasarian said the Trump administration’s 2025 funding cuts to the Centers for Disease Control reduced Michigan’s public health staff by over 100 workers and have “absolutely” slowed the current investigation.
The cyclosporiasis outbreak is a “canary in the coal mine” for a public health system “stretched to the breaking point” by funding cuts and staff shortages, said Levy, the University of Washington researcher.
The CDC did not respond to a request for comment. The FDA said in a statement to the FT that it is “currently investigating Cyclospora outbreaks using established epidemiological, laboratory and traceback tools in close co-ordination with the CDC and state and local partners”.
No deaths are associated with the cyclosporiasis outbreak, but hundreds have been hospitalised for cases of gastrointestinal distress including explosive diarrhoea, which can last up to a month without treatment.
The figure for the decline in Taco Bell foot traffic in this article has been amended following an update from the data provider.
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