A cyclosporiasis outbreak in at least 30 states is causing gastrointestinal misery for thousands.
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It’s been a relatively hot summer in many parts of the United States. The hotter than normal weather could have played a role in exacerbating this summer’s clusters of cyclosporiasis which have now been detected in 31 states. It’s possible that the decadeslong trend of rising temperatures globally is contributing to the more frequent presence of diseases more typically found in tropical regions.
The official tally on July 9 at the Centers for Disease Control and Prevention was 843 confirmed domestic cases of the diarrheal disease, with 86 hospitalizations and no deaths. But this is an undercount, as the state of Michigan alone has reported as of today, July 14, more than 3,300 cases since June 22. The CDC’s number merely comprises cases reported by states directly to the agency.
According to CNN, public health officials in Michigan suggest that the ongoing outbreak may be linked to lettuce and other salad greens. But they haven’t ruled out other foods. Nor have they identified a “specific type, grower or supplier” as the source.
The causal agent in cyclosporiasis is a microscopic parasite called Cyclospora cayetanensis, which can spread through food or water contaminated with human feces. Usually, contamination happens on farms. According to the CDC, cyclosporiasis occurs seasonally in many countries worldwide but is most common in tropical and subtropical regions.
The disease doesn’t spread person-to-person. National Geographic writes that “people get sick around a week after eating contaminated food — most commonly fresh produce, especially raspberries, leafy herbs, and bagged salad mixes — but it can take as little as two days and as long as two weeks to develop symptoms.”
Though the disease is generally not life-threatening, cyclosporiasis symptoms can last for weeks, having the potential to cause particularly severe problems in young children, older adults and immunosuppressed people. Symptoms are characterized by watery, often explosive diarrhea, stomach cramps, nausea, fatigue and weight loss.
Cyclosporiasis is less common than other kinds of better-known foodborne illnesses, such as salmonella and E. coli. Historically, outbreaks have often been seasonal, with, for instance, salmonellosis most commonly reported in summer.
A Possible Role for Climate Change
Climate change appears to be altering the timing of recurring natural phenomena like the emergence of buzzing cicadas in summer. They start making their unique piercing sound about 14 days earlier on average than 20 years ago in places like the Northeastern U.S.
Similarly, global warming may also be lengthening the seasonal transmission window of certain bacteria and viruses that cause gastrointestinal illnesses. In this vein, public health experts have long warned that a warming climate could contribute to larger spikes in the spread of cases of diseases such as cyclosporiasis.
Up until around a decade ago, periodic cyclosporiasis clusters occurred annually scattered around the country during the summer months. But they weren’t especially large in terms of numbers of cases. The numbers of outbreaks and cases then began to rise, with conspicuous spikes in 2018 and 2019 and now in 2026. Experts attribute the increases to better testing and detection methods but also climate change or long-term shifts in temperatures and weather patterns.
Scientists have formally hypothesized a role for climate change in creating more optimal environmental conditions needed for diseases such as cyclosporiasis to spread. They observe associations between higher temperatures in non-tropical settings and the prevalence of pathogens such as cyclospora. Indeed, cyclospora depend on prolonged outdoor heat and moisture to mature, which makes it sensitive to the effects of rising temperatures.
Geographic expansion owing to climate change may facilitate the process by which cyclospora become increasingly prevalent in the U.S. And this doesn’t just apply to foodborne infectious diseases. To illustrate, the warming trend has helped establish West Nile virus, caused by bites from infected mosquitoes, as an endemic disease across the U.S. in the past 25 years. Likewise, Europe is experiencing a significant increase in prevalence of West Nile and other tropical diseases.
Research shows that continued climate change could help increase the transmissibility of viruses such as West Nile, which is part of a family of vector-borne viruses that includes Zika, dengue and yellow fever.