Florida – Outbreaks of the H1N1 flu among children attending U.S. summer camps presage a surge in cases this fall as students return to school, an official at the U.S. Centers for Disease Control and Prevention warned on Wednesday.

This is just a harbinger of what we will see in the fall, Dr. Richard Besser, who led the U.S. response to the virus outbreak last spring, told a meeting of public health officials.

Besser, who was the CDC's acting director for the first half of this year, later told Reuters that the number of outbreaks in summer camps was in the hundreds.

He predicted soaring numbers of H1N1 cases compared to those seen in April when the first U.S. cases were diagnosed in California and urged health officials to plan now for the possibility of crowded hospitals, swamped emergency rooms and overwhelmed clinics.

The magnitude of the event in the fall will be much greater (than what was experienced last spring), Besser said.

Besser and local health officials from around the country strategized on how to best respond to the fast-spreading virus during the opening day of the National Association of County and City Health Officials annual conference in Orlando.

Local health officials, who plan and regularly practice their response to hypothetical public emergencies, nonetheless raised concerns about the logistics of sustaining an emergency response to an expanding pandemic and mass vaccination campaign this fall.

A big worry is inadequate staffing and the problem of exhaustion among those on the front lines.

We all assume we can go home in 48 hours (as in a practice drill) but this may last all winter, said a health official from Portland, Oregon.

Besser advised health officials to consider pausing other activities in their departments to free up staff to help with the H1N1 response.

H1N1 swine flu is now so widespread that the World Health Organization (WHO) has stopped counting individual cases.

So far H1N1 is characterized by mild symptoms in most patients who go on to recover without treatment within a week.

The median age of sufferers has been 14 to 17 years old, although the age is increasing slightly as the number of cases increases, according to the WHO, suggesting the virus is spreading from schools into the wider community.

(Editing by Jane Sutton)