Rise in Stomach Illness Cases Reported in Southeastern Ontario

A hospital sign is seen at a facility in southwestern Ontario on May 22, 2025. The Canadian Press/Nicole Osborne

Cases of infectious gastrointestinal illness are increasing in southeastern Ontario, with norovirus accounting for most infections, local public health officials say.

Ontario’s Southeast Public Health said in a May 4 news release that stomach illnesses are on the rise in the Kingston area and are highly contagious. The agency is advising residents to take precautions to limit further spread.

In a separate update on May 1, Southeast Public Health said 11 long-term care facilities and retirement homes in the region had suffered outbreaks. All but one were respiratory, and two outbreaks had been declared over. Four were listed as involving an unknown pathogen, while one was linked to SARS-CoV-2, the virus that causes COVID-19.

Symptoms may include diarrhea, nausea, vomiting, stomach cramps, fever or fatigue. People are urged to stay home for at least 48 hours after symptoms have stopped. The public is also advised to wash hands frequently and avoid public pools and hot tubs while ill, the release said.

Norovirus is responsible for 90 percent of stomach flu cases, according to the Public Health Agency of Canada. The virus is a leading cause of foodborne outbreaks globally and is most commonly linked to settings such as schools, hospitals, restaurants, long-term care homes, daycare centres and travel-related venues, including cruise ships.

Stomach flu—a common term for viral gastroenteritis—is typically seasonal, with cases peaking in the colder months from late fall through early spring. Public health officials note that outbreaks tend to increase during this period as people spend more time indoors in close contact, creating favourable conditions for transmission.

The broader respiratory virus season has also been active in Ontario. According to Public Health Ontario, the 2025-26 season saw an early and sharp rise in influenza, with 5 percent of tests returning positive in mid-November and 35.7 percent in mid-December. Influenza A, particularly A/H3N2 (subclade K), was the dominant strain, while influenza B circulated later at lower levels. Children aged 5 to 11 recorded the highest rates of infection, followed by those aged 12 to 19.

Although weekly cases, hospitalizations, and outbreaks were higher during the peak of this season than in recent seasons, officials said the overall shorter duration of the wave meant the total impact was comparable to or lower than in 2024–25.