A microscopic parasite found in contaminated food is ruining summer meals across the United States in the largest outbreak of its kind in the country's history — and health officials have yet to identify the source.
Since May 1, 1,645 infections with Cyclospora cayetanensis have been confirmed, with more than 5,100 additional cases under investigation, according to the U.S. Centers for Disease Control and Prevention. These figures have accumulated in just a few weeks, quickly surpassing the total number of cases typically seen in an entire year.
More than 100 people have been hospitalized, though no deaths have been reported yet. Michigan has reported the highest number of infections, with state officials signaling that lettuce or salad greens could be the culprit.
The diarrhoea-causing parasite invades the lining of the intestines, rapidly multiplying and damaging cells. The hallmark symptom of watery diarrhoea can last for weeks or even months. The main treatment is the antibiotic trimethoprim-sulfamethoxazole (Bactrim), which starves the parasite of an essential vitamin it needs to replicate.
Contamination generally occurs through sanitation failures — raw sewage run-off contaminating agricultural soil, or farm workers lacking access to toilets near crop fields. Although Cyclospora is most common in tropical climates and past U.S. outbreaks were frequently tied to imported foods, it is increasingly becoming a domestic issue.
What worries researchers is the trend: outbreaks seem to be getting larger year by year. Climate change, creating warmer environments for the parasite's oocysts to mature, could be partially to blame.
Joel Barratt, a molecular parasitologist at Emory School of Medicine who worked at the CDC for eight years, told Nature the investigation is likely being hampered by staffing cuts. "The number of staff working on these outbreaks is not what it used to be," he said, noting he left the agency after the Trump administration downsized the government.
Health officials are coordinating with state and federal laboratories, collecting faecal samples and tracking what patients ate in the weeks before symptoms appeared. However, the source remains elusive.
