Ontario's number of swine flu cases almost doubled on Monday as the virus spread beyond the Greater Toronto Area to Windsor, Barrie and Sudbury, but all 31 cases were mild and the people were recovering at home without having been admitted to hospital.

Dr. David Williams, the province's top medical official, said there were new confirmed cases of the H1N1 virus in Oxford and Simcoe regions, Sudbury, and Windsor-Essex as well as in and near the city of Toronto.

One was a four-year-old child, while another was a high school student at St. Joan of Arc High School in Barrie.

The Simcoe Muskoka Catholic District School Board said health officials confirmed the case was mild and that the contagious period had passed. Williams said there is no need to close schools in Ontario.

Twenty-five of the 31 known cases have a travel history to Mexico, while the travel details of five other Ontario cases were still being confirmed.

There were 140 confirmed cases of swine flu nationwide Monday, including a young girl in Alberta with a severe case who was hospitalized — a first for Canada.

The fact that the number of Ontario cases virtually doubled overnight was not a major concern, said Williams, who admitted the numbers will keep rising in the short term.

"I was expecting the numbers to be coming up, so I'm not surprised we had these now," he said.

"We've had a large load in the laboratory coming through, a lot more tests to come forward, so I'm going to expect some more numbers up in the next few days."

Limited spread of virus

So far there's been only one confirmed case of swine flu transmitted person to person in Ontario, and one other under investigation, but that doesn't mean there should be any fears the virus is being spread in communities, said Williams.

"The one that we have and one that is under investigation are very close family contacts, so we're not seeing widespread transmission," he said.

"Like we've seen in a few of the states where family-to-family [transmission] has occurred, that is not surprising."

Ontario reported 17 new cases of swine flu Monday, and two earlier reported cases were being re-evaluated after being added to the list Sunday before their lab results were in.

The province is testing up to 350 samples to determine additional cases of swine flu, said Williams.

The average age of the Ontario victims remains about 24, but ranges from as young as four to 50 years old. There are 11 males and 20 females in the province with confirmed cases of the flu.

Ontario previously reported cases in Toronto and Peel, Durham and York regions.

Canadian health officials cautioned people not to worry if the World Health Organization raises its pandemic alert level from five to six, because it just means the UN agency sees evidence of sustained transmission in a region outside of North America.

"We already have sustained community transmission in our region," said Dr. Vivek Goel, the CEO of Ontario's Agency for Health Protection and Promotion.

"So the move from five to six is more relevant for countries that don't yet have any circulating influenza."

The Public Health Agency's website says on average, the common flu sends about 20,000 Canadians to hospital each year. Between 4,000 and 8,000 Canadians can die of influenza and its complications annually, depending on the severity of the season.