TORONTO - A health official says cases of swine flu have been confirmed at three Ontario summer camps and more than 225 children have symptoms of H1N1.

The cases, all said to be mild, are in the central Ontario region of Simcoe-Muskoka. The Simcoe-Muskoka District Health Unit says none of the affected campers have required hospitalization.

The Olympia sports camp, just outside of Huntsville, reported on its website that it had one confirmed case of swine flu and other campers with respiratory infections.

The posting says the camp remains open on the advice of health officials and a new group of campers began their session on July 12.

The region's acting associate medical officer of health says only a small number of cases at the three camps are laboratory confirmed as swine flu but adds the campers are assumed to have contracted H1N1 based on their symptoms.

Dr. Na-Koshie Lamptey would not say which other camps are involved but added parents with children at the camps have been notified.

Those detected with the flu-like symptoms represent almost 20 per cent of the children at the three camps.

There are no plans to close any camps because of the flu.

Parents are being urged to screen their children for symptoms of the flu before sending them to camp.

Provincial guidelines issued last month say summer camps have the potential to be a high-risk setting for transmitting swine flu because children and young adults are in close quarters for extended periods of time.

The guidelines say a day camp experiencing more than 10 per cent of campers or staff ill or absent due to influenza-like illness should be considered to have an outbreak.

In the case of camps with children with special needs, the guidelines say one case of swine flu may be enough to be considered an outbreak given the high-risk nature of the campers.

An Ontario Ministry of Health spokesman it is the responsibility of the local health units to monitor cases at summer camps.

"From our point of view we expected that this had the potential of happening," said David Jensen, who added the cases at the three camps are "mainly localized."