Toronto Public Health says norovirus may be the cause of an outbreak that has affected more than 200 students at a city college, but the agency is waiting for laboratory confirmation.

Dr. Michael Finkelstein, an associate medical officer of health at the agency, says the illness was first reported to public health on Friday, after 40 people at a Humber College campus were sent to hospital.

He says that so far, 50 people have been sent to hospital, but only one person has been admitted for treatment of dehydration. The rest were examined in the emergency room and then released.

Most of those affected live in the college's north campus residence, which houses about 1,000 students.

Finkelstein says those affected by the illness experienced symptoms such as vomiting, diarrhea, dizziness and abdominal pain, which are consistent with norovirus.

He says norovirus is highly contagious, causes severe symptoms quickly, but it also goes away very quickly.

A spokesman for the college said on Friday that students began reporting symptoms around 3:30 p.m. on Thursday, with more cases surfacing through the night. At that point, there were only about 77 reported cases.

While the setting of the outbreak may be somewhat unusual -- Finkelstein said that he'd never investigated an outbreak on a college campus before -- it isn't necessarily surprising.

"When you bring this number of people in a small space like a college residence, certainly that does increase the risk of a virus like norovirus spreading from person to person."

"They're using common bathrooms," he added, which presents ample opportunity for germs to spread if sinks and toilets aren't cleaned between uses.

A representative from the college said common areas are now being cleaned more often, and Finkelstein said students should be sure to properly clean their living spaces to prevent the disease from spreading further.