The Centers for Disease Control and Prevention offices in Atlanta are seen in 2022. The agency is investigating a rise in cyclosporiasis cases.

Ron Harris/AP

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Ron Harris/AP

An outbreak of an intestinal disease that causes diarrhea, nausea and fatigue has been detected in 31 states, but the source is still under investigation, according to federal health authorities.

As of Thursday, the Centers for Disease Control and Prevention saying had received reports of 843 cases of cyclosporiasis, the gastrointestinal disease caused by the parasite cyclospora.

But the actual number of infections is likely much higher, because that figure only represents cases reported by states directly to the CDC. There is also a lag between the onset of symptoms and their reporting, and many people recover from the disease without medical treatment. Michigan alone reported 1,562 cases of cyclosporiasis until Friday.

As of Thursday, there have been 86 hospitalizations nationwide and no deaths, according to the CDC.

People can get the disease by eating food or drinking water contaminated with the parasite. Previous outbreaks have been linked to fresh produce. In 2018, McDonald’s removed salads from restaurants in 14 states after federal health officials linked them to dozens of cases of cyclosporiasis, and contaminated lettuce imported from Mexico was suspected of sickening 400 people in the United States in 2013.

It is typical for cyclosporiasis infections to increase in the spring and summer, but the CDC said Friday that several states had reported a larger increase in cases during the previous two weeks than during the same period last year.

Where do cyclosporiasis infections occur?

Health officials from California to Texas and Florida have reported cases of cyclosporiasis since early May.

Some of the hardest hit areas appear to be in the Midwest and Northeast, including Michigan and New York.

Ohio Department of Health reported 177 cases of cyclosporiasis as of July 2, most of which occurred in June. Dr. Bruce Vanderhoff, director of the Ohio Department of Health, said cyclosporiasis is a “serious illness that can cause dehydration and requires people to seek emergency medical care, and should be taken seriously.”