'Explosive' diarrhea parasite sickens more than 1,000 in U.S. Should Canadians be concerned?

A diarrhea-causing parasite has infected more than 1,000 in the U.S. Is it in Canada?

Cases have surged in Michigan over the last week

A diarrhea-causing parasite has led to a growing outbreak in the United States that has sickened more than 1,000 people and sent dozens to hospital.

As of Wednesday, multiple states had reported cyclospora infections, which can cause watery diarrhea, bloating, fever and nausea.

While cases are common in the spring and summer, the current outbreak has led to an unusually high number, making it one of the largest the country has seen. No deaths have been reported.

Despite the rapid growth of the outbreak, a spokesperson for the Public Health Agency of Canada (PHAC) said the agency is not investigating any outbreaks in Canada and that the parasite is "not commonly found on food and is not in drinking water in Canada."

Cyclospora is a microscopic, spherical parasite that commonly causes watery diarrhea "with frequent and sometimes explosive bowel movements," according to the U.S. Centers for Disease Control and Prevention.

The illness, called cyclosporiasis, is not usually life-threatening and can be treated with antibiotics.

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

"This is a disease that is typically transmitted through fresh fruits and vegetables, especially those that have nooks and crannies, things like raspberries and blueberries, lettuce," said Lawrence Goodridge, a food safety professor at the University of Guelph.

While it remains unclear what is behind the outbreak, Goodridge expects it is linked to produce imported from South and Central America, the Caribbean, Southeast Asia or Africa.

Symptoms can begin up to two weeks after exposure and last as long as two months, Goodridge said.

Cyclospora is less common than several other foodborne illnesses, including salmonella and E. coli. For years, few U.S. cyclospora outbreaks were reported annually. But the number began rising about a decade ago, with particularly notable spikes in 2018 and 2019. Experts attribute the increases to climate change and improved detection.

On Wednesday, Michigan reported about 992 cases, including 40 hospitalizations — a significant increase from when officials first announced the outbreak last week. Most cases have been concentrated in the southeastern part of the state.

Michigan typically records about 50 cases a year.

Just across the state line, Lucas County, Ohio, had reported 306 cases as of Wednesday. Northwest Ohio has recorded more than 400 cases.

There are 28 other states, including Illinois and New York, that have reported cases and are investigating.

The source of the outbreak has not been identified, and experts say it is often difficult to trace.

"Any outbreak of foodborne illness caused by fresh fruits and vegetables, it's always challenging because the shelf life of those products is short," said Goodridge.

Despite the surge, the outbreak is not considered a national health emergency.

There is no evidence that the parasite has evolved to become more infectious, said Dianna Blau, acting chief of the CDC's parasitic diseases branch.

Thousands of cyclospora illnesses are reported in the U.S. each year, and it's not yet clear how unusual this year will be, she added.

Michigan appears to be experiencing the largest concentration of cases, but the state's aggressive reporting may be "part of the reason why this looks like a Michigan problem," said Dr. Natasha Bagdasarian, Michigan's chief medical executive.

Previously large outbreaks include one in 1997 tied to Guatemalan raspberries that sickened more than 1,000 people in the U.S. and Canada, and a 2019 outbreak linked to Mexican basil that sickened more than 2,400.

While the current outbreak is not affecting Canada, the federal government says an average of 238 cyclosporiasis cases were reported each year between 2004 and 2019.

"I don't think Canadians should be worried that this outbreak could come into Canada," said Goodridge.

Anyone who suspects they may be sick should seek medical care and testing, Goodridge said.

Canadians travelling to the U.S. should avoid fruits and vegetables, or eat only cooked produce and fruits that can be peeled or have smooth surfaces, such as grapes, Goodridge said.

Washing produce will not protect against the parasite, he said.

He also recommended buying whole heads of lettuce so the outer leaves can be removed. Freezing fruit can reduce the parasite, he said, but there is no guarantee it will eliminate it.

Jennifer La Grassa is a videojournalist at CBC Windsor with a focus on health-care stories. Have a story? Email jennifer.lagrassa@cbc.ca

With files from The Associated Press