A fast-moving US outbreak of cyclosporiasis, a parasitic gut infection most often linked to raw produce, has reached nearly 7,000 potential cases, according to the Centers for Disease Control and Prevention. More than 3,300 of those cases were in Michigan as of Tuesday, where state officials have pointed to contaminated lettuce as the likely source.
The official count is probably a low-resolution snapshot, not the full map. Jeanne Marrazzo, CEO of the Infectious Diseases Society of America, said many people with diarrhea do not seek medical care. Even when they do, labs do not routinely screen for cyclospora because it is less common than other foodborne pathogens and is not included in many standard gastrointestinal test panels.
Marrazzo estimated that the real number of infections is at least twice the CDC figure, citing underdiagnosis and mild cases that never enter the reporting system. For patients who do get hit hard, she said, the illness can last far longer than a typical bout of diarrhea and can keep people out of normal life for a while.
Why washing produce may not be enough
Public health officials have advised people to wash produce thoroughly. Some restaurants have also changed what they serve. Taco Bell said it temporarily removed a limited set of ingredients at selected restaurants as a precaution, according to the Associated Press.
That kind of step may reduce exposure in specific locations, but the parasite is an unpleasant fit for the modern produce chain. Norman Beatty, an associate professor of medicine in infectious diseases and global medicine at the University of Florida, said cyclospora can lodge in crevices on fruits and vegetables. He said it is most often found on fresh produce eaten raw, including herbs, lettuce and berries.
The infectious form of the parasite, called an oocyst, is also hard to remove with the industrial washing systems shoppers tend to imagine as a magical produce reset button. Beatty said cyclospora resists bleach and common sanitizers used by food manufacturers, allowing oocysts to remain stuck to produce even after commercial washing.
Cooking kills the parasite, according to the experts cited. That is useful for some foods and almost useless for the items most associated with cyclospora, because lettuce and berries are commonly eaten raw.
Water may be the bigger problem
Bill Marler, a lawyer who specializes in food poisoning cases, said cyclosporiasis cases have historically been linked mainly to imported produce. Over the past decade, however, the US has seen domestic cyclospora outbreaks, including one tied to bagged lettuce from an Illinois plant that sickened more than 700 people.
Marler said the pattern points away from the tidy morality tale of one farmworker failing to wash their hands. He said contamination is more likely to involve water used to irrigate crops, which would explain how the parasite can spread across a larger volume of produce.
That is the grim feedback loop public health officials worry about: infected people shed cyclospora, contaminated water can reach crops, and distributed produce can seed cases far from the original contamination point. The parasite also resists chlorine, the main disinfectant used in many municipal water and wastewater systems, according to Beatty.
Beatty said thousands more people across the country are likely infected. He also said the outbreak could be reported in all 50 states because US food distribution networks can move a contaminated organism from one location to many others quickly. That is a forecast, not a confirmed case map. The confirmed numbers remain the CDC’s nearly 7,000 potential cases, with Michigan accounting for more than 3,300.
This story draws on original reporting from WIRED.
