Seventeen Montreal hospitals and long-term care facilities are dealing with an outbreak of gastroenteritis.

Several of the facilities, including the city's largest hospital, Maisonneuve-Rosemont, have been forced to isolate patients to prevent a further spread of the virus causing the ailment, commonly known as the stomach flu.

Although the virus has also been present in the general public in seasonal form since early February, gastroenteritis is more troubling to treat in people who are already in hospitals, said Dr. Alexandra Kossowski, head of transmittable diseases at Montreal's public health department.

"It's more dangerous for people that are in a hospital because their immune system is weaker," Kossowski said.

"They are more prone to get serious dehydration, and also the fact that they're in a closed area, it spreads more easily."

The virus is usually spread person to person and through contaminated food and objects, Kossowski said.

Symptoms include nausea, vomiting and diarrhea, and last on average 48 hours.