Ontario has had three more deaths associated with swine flu since Monday, raising the province's total to seven, the province's chief medical officer of health said Wednesday.

A 17-year old male from the Ottawa region, a 52-year old woman from eastern Ontario and a 68-year old man from the Durham region all tested positive for the H1N1 flu virus, Dr. Arlene King confirmed.

All three had underlying health conditions. It's not clear what role the virus may have played in the fatalities.

The Office of the Chief Coroner is also investigating the death of a six-year-old girl announced earlier this week in Brampton. Her parents reportedly took her to see a doctor when she first showed signs of a fever. Later that evening, she collapsed and died in her parents' car en route to hospital.

"Somebody who does develop H1N1, fever, feeling lousy, bit of a cough, not getting better, or gets better and then gets worse again, that's time to seek medical attention," said Dr. Donald Low, head of the department of microbiology at the University Health Network and Mount Sinai Hospital in Toronto.

"It has been described in the past where you can actually have co-infections," said Low. "Not only influenza, but you can have certain other types of bacteria. And the two of them together have this overwhelming presentation [of pneumonia], which has occurred in prior pandemics and also prior influenza years."

The rare death of a child with swine flu out of probably tens of thousands of cases in Canada is reassuring, given that laboratory findings also show no signs that the influenza A H1N1 virus is becoming more virulent, Low said.

"There continues to be a lot of activity with the H1N1 flu virus and Ontarians should remain vigilant in monitoring their health and those of their loved ones," King advised in a release.

"People can protect themselves and those around them by washing hands frequently, coughing or sneezing into their sleeve and staying at home if they are sick."

As of Monday, the total number of cases in the province was 2,665. Almost all have shown symptoms similar to seasonal influenza, and the majority have recovered.

As of Tuesday, 28 people with H1N1 were in hospital, including several with underlying medical conditions.

Across Canada as of Monday, 6,457 laboratory-confirmed cases of H1N1 flu virus have been reported to the Public Health Agency of Canada. To date, 404 hospitalizations and 15 deaths have been reported among laboratory-confirmed cases.

The World Health Organization reported Wednesday that there 55, 867 cases worldwide, including 747 new cases in Canada.

But Low noted that seemingly high number of Canadian cases likely reflects extensively testing for swine flu, compared with poorer countries that lack testing infrastructure.