A widespread outbreak of cyclosporiasis, a gastrointestinal illness caused by a foodborne parasite, continues to grow in the United States as health authorities seek to determine its source. Michigan, the epicenter of the outbreak, reported over 400 new cases on Tuesday, bringing its total since June 21 to 6,571—dramatically surpassing the state's typical annual average of around 50 cases. Other Midwestern and Northeastern states have also reported hundreds of cases.

The Michigan Department of Health publicly acknowledged increased cyclosporiasis cases on July 1. Early investigations implicated lettuce supplied by Taylor Farms to Taco Bell restaurants, prompting the fast-food chain to voluntarily remove Taylor Farms lettuce from its nationwide menus. However, the Food and Drug Administration (FDA) later retracted initial laboratory findings that detected Cyclospora parasites on Taylor Farms lettuce, characterizing the results as a false positive.

Despite the FDA’s withdrawal of the positive test result, Michigan health officials maintain that epidemiological data still indicate a strong link to lettuce or salad greens as the likely source of infection. Nevertheless, some patients have reported neither consuming lettuce nor dining at known implicated chains, leading health officials to consider the possibility of multiple sources contributing to the outbreak.

Taylor Farms has continued its recall of iceberg lettuce grown in central Mexico and announced it will avoid sourcing from that region for the remainder of the growing season. Both Taylor Farms and Taco Bell have not provided comments regarding the ongoing investigation.

Experts note that detecting Cyclospora in laboratory tests is notoriously challenging, with a high potential for false positives. Karen Levy, a University of Washington professor specializing in foodborne illnesses, described the outbreak as a warning sign for an overstretched public health system.

Michigan’s chief medical executive, Natasha Bagdasarian, emphasized that last year’s reductions in federal funding to the Centers for Disease Control and Prevention (CDC) led to the loss of more than 100 public health staff in the state, which has hindered investigative efforts. The CDC has not commented publicly, but the FDA stated that it is actively investigating the outbreaks using epidemiological, laboratory, and traceback methods in coordination with the CDC and state and local partners.

To date, no fatalities have been reported in connection with the outbreak. However, hundreds of patients have required hospitalization due to severe gastrointestinal symptoms, including explosive diarrhea that can persist for up to a month without treatment. Health authorities continue to monitor the situation closely as efforts to identify and control the contamination source remain underway.