Two people have died in the cyclospora outbreak in Michigan, state health officials announced Monday, the first deaths confirmed in the U.S. related to the microscopic parasite.

The Michigan Department of Health and Human Services said both people had underlying health conditions that may have been impacted by the intestinal illness and dehydration. The department said it would not provide additional information about the deaths.

Cyclospora is a microscopic, spherical parasite that commonly causes watery diarrhea “with frequent and sometimes explosive bowel movements,” according to the Centers for Disease Control and Prevention. Outbreaks tend to occur most often in the late spring and summer.

The CDC says the illness, called cyclosporiasis, is rarely deadly.

The heat-loving parasite infects the bowels and spreads through feces. In the past, people have been infected by consuming fruits or vegetables that were exposed to feces-contaminated irrigation water.

Cyclosporiasis is less common than other foodborne illnesses, including salmonella and E. coli. Many cases are never linked to a specific food or other source and, for years, few U.S. cyclospora outbreaks were reported. But the number started rising about a decade ago, with a particularly notable spike in 2018 and 2019.

Previously, 2019 saw the most reported U.S. cyclosporiasis cases, with about 4,700.

Since May 1, the CDC has received reports of more than 4,100 confirmed cases and is investigating more than 7,400 other likely cases across 41 states. The agency has warned that the total number of people sickened by the outbreak is likely higher than the official tally, given that not all cases are reported.

Federal health officials have identified lettuce from Mexico served at Taco Bell locations in nine states as a source of the widespread outbreak. As of late July, the number of cases linked to the lettuce was 1,947, including at least 98 people who had to be hospitalized, according to the CDC.

The agency has said other “brands, restaurants, retailers, or distribution channels” could be tied to the outbreak as the investigation continues.

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Associated Press reporter Mike Stobbe in New York City contributed.