Summer playgrounds may pose flu risk in NYC - mayor

*New York offers model of H1N1 for other big cities

*Summer camps, playgrounds may spread virus

NEW YORK, June 12 (Reuters) - Cases of the new H1N1 flu virus are declining in New York, one of the U.S. cities hit earliest and hardest by the new pandemic virus, health officials said on Friday.

But New York mayor Michael Bloomberg said he worried that children may carry the virus to playgrounds while they are on holiday from school in July and August.

New York reported three more deaths from the swine flu on Friday, bringing the city’s total to 16, with 567 hospitalizations -- by far the highest rate in the United States, which, with around 1,000 people hospitalized with H1N1, is the country with the most cases overall.

“While every hospitalization is concerning and every death is a tragedy, our surveillance data indicate that the number of people newly infected is declining,” New York City Health Commissioner Dr. Thomas Farley said in a statement.

The World Health Organization declared a full pandemic of H1N1 on Thursday after confirming the illness was spreading out of control not only in North America, but in Australia. U.S. health officials estimate that hundreds of thousands of people are infected, although the WHO classifies the virus as “moderate.”

The swine flu virus, first identified in two U.S. children in April, caused a cluster of cases associated with a New York school and then spread across the city of more than 8 million people. The U.S. Centers for Disease Control and Prevention said on Thursday the states with the highest H1N1 activity are New York, New Jersey and Massachusetts.

The CDC has confirmed 17,855 cases of H1N1 and 45 deaths but said the actual numbers are far higher as most patients are not tested and many may not even visit doctors.

Bloomberg said New York also had a surge of the so-called worried well -- people who believe they may have a disease and visit clinics and emergency rooms when they do not need to.

“The good news is (there are) fewer of the worried well,” Bloomberg said on a weekly radio show. “The number of hospital visits is down and the numbers of kids reporting to the school nurses with fevers is way down.”

CDC officials said last month that while flu season usually ends in April, past outbreaks have been associated with summer activities such as summer camp. Bloomberg said he feared this could happen this year in New York.

“Kids in the summer congregate in different ways; one theory is it’s more dangerous in the summer because kids come from different locations to get together,” he said.

The last day of school for public school students in New York City is June 26.

CDC and WHO officials expect H1N1 activity to calm during the warm summer in the northern hemisphere but caution that flu is unpredictable. This virus, like other H1N1 viruses, affects people younger than 45 more than other flu viruses do.

Other pandemic viruses have begun with mild epidemics in spring, only to cause serious disease months later, when cooler weather returns.

Editing by Patricia Zengerle