Canada reported three new cases of swine flu on Wednesday, bringing the total number to 16.

Public health officials say the new cases are all mild and all are in Ontario province, which already have four cases. All three cases are women in their early 20s and all have mild versions of the flu.

Of the seven cases in Ontario, six recently returned from Mexico and it remains unclear whether the seventh had been to Mexico recently, David Williams, the chief medical health officer of the province said at a press conference in Toronto.

The other Canadian infections are in British Columbia, Nova Scotia and Alberta.

Canada's biggest challenge in dealing with the swine flu outbreak is to track down the thousands of Canadians who returned from Mexico in the last few months and may have contracted the disease, says one expert.

Mexico is the second-most popular destination among Canadian travelers, with more than 1 million people visiting Mexico every year.

Donald Low, an infection disease specialist at Mt. Sinai Hospital in Toronto, said the challenge here is to locate and identify Canadian cases in order to get a handle on how widespread the disease is in Canada.

He said the goal is to track down those who are infected, give them the information and instruction they need to avoid infecting others, and to collect specimens to "get a sense of how much disease is out there."

He said it is too late to contain the disease, and efforts have turned to mitigating the damage and reducing the impact on people's health.

Canada has issued a travel advisory against all non-essential travel to Mexico. Following that, several big travel companies canceled trips to Mexico.

Transat AT said all flights to Mexico will be canceled until at least June 1.

Air Canada and Air Canada Vacations also announced on Tuesday they will suspend all operations to Cancun, Cozumel and Puerto Vallarta, Mexico, until June 1. The airline said, however, it will keep its flights to Mexico City going.

(Xinhua News Agency April 30, 2009)