‘Watery diarrhea’ cases surge in Quebec, as Michigan identifies lettuce as possible source of outbreak

Cases of cyclosporiasis in Michigan, bordering Ontario, increased by more than 500 reports in a single day to reach 4,312, according to state health officials. Meanwhile, the number of Quebecers who have the parasite has jumped by 166 per cent.

A mounting outbreak of the foodborne illness with an unknown source that can cause weeks of severe, “watery diarrhea,” stomach cramps, bloating and fatigue may have sickened nearly 7,000 people in the United States, according to the Centers for Disease Control and Prevention.

Michigan has been hardest hit by cyclosporiasis, and state health officials are considering “lettuce or salad greens” as a potential source of the recent outbreak.

While “nowhere near the scale of the outbreak reported in the state of Michigan,” 85 cases have been reported in Quebec since the beginning of the year, up from an annual average of 32 cases during the same period from 2022 to 2025, according to the province’s health ministry.

“An excess of cyclosporiasis cases is being observed in Quebec in 2026,” the ministry reportedly said in a statement Tuesday.

As is the case in the rest of the country, most of Quebec’s cyclosporiasis cases were previously travel-related — ”primarily to Mexico.” In the recent surge of cases, however, fewer than five reportedly travelled to the United States. None of the people affected in Quebec “appear to be associated with the ongoing outbreak in Michigan,” the ministry added.

In Canada, an average of 298 cases of cyclosporiasis were reported annually between 2004 and 2023. The Public Health Agency of Canada (PHAC) said in an email to National Post on July 13 that it “is not currently investigating any Cyclospora outbreaks in Canada.”

Cyclosporiasis results from infection with the parasite Cyclospora, which is transmitted through feces-contaminated food and water. “Cyclospora is not commonly found on food and is not in drinking water in Canada,” according to PHAC. The agency noted that there’s typically an increase in infections during the spring and summer as people eat more imported fresh fruit and vegetables.

In a health alert issued on July 14, the CDC reported 1,645 confirmed cases of cyclosporiasis since May 1. Nine per cent (141) were hospitalized, and no deaths have been reported. More than 5,100 cases are under investigation.

“This is substantially higher than the 249 cases reported nationally by this same time last year,” according to the alert.

As of Thursday, health officials in Michigan had reported 4,312 cases and 102 hospitalizations. The investigation into the outbreak is ongoing, and while they’ve identified “lettuce or salad greens” as the potential culprit, officials warn that “other food items cannot be completely ruled out. No specific type of produce, grower or supplier has been identified as the source.”

Other fresh fruits and vegetables, including basil, cilantro, raspberries, snap peas and snow peas, have been linked to previous cyclospora outbreaks.

To reduce risk of illness, Michigan officials advised buying whole heads of lettuce instead of prepared salad bags or kits, discarding the outer layers and washing the inner leaves well under running water.

Washing can reduce its numbers, but it won’t eliminate the parasite. As Keith Warriner, a professor at the University of Guelph’s department of food science, told National Post, “(Washing) is not going to do that much” to remove Cyclospora, E. coli or Salmonella.

PHAC recommends sourcing fresh produce grown in Canada, “especially during the spring and summer months when an increase in Cyclospora infections linked to consuming fresh fruit and vegetables imported from other countries are reported.”

Cyclospora is most common in tropical and subtropical regions. When it comes to fresh produce imported from countries with the parasite, cooking (to at least 70 degrees Celsius) or freezing (at -20 C for roughly seven days) are your best bets.