The flu usually appears in November, December and January and leaves in March, April and May.

"Once in a while it arrives early, then goes away and comes back in earnest," said Dr. Richard L. Vogt, chief of the state health department's communicable disease division. "That's probably the scenario we're going to see here."

Older residents and those with heart and lung problems are most vulnerable, he said.

He said a total of 63 confirmed cases have been reported to date - mostly before Aug. 9, when Island physicians received a state Health Department advisory that flu had arrived.

Four were influenza B cases and the rest influenza A, he said. Both produce mild to severe illness, although they are different strains, he said. The big difference: Anti-viral medication doesn't work for influenza B.

Vogt said the staff and patients of an unidentified nursing home were affected. Tripler Army Medical Center also had an unusual number of cases, and private doctors, primarily on Oahu, have reported a number of cases.

Maj. Bill Nauschuetz, Tripler epidemiologist, said the hospital confirmed 20 influenza cases in the past two months.

Only one influenza case was recorded at Tripler in July and August for the entire four years until now - "an indicator that we're obviously seeing something uncommon," he said.

Vogt noted that Australia and New Zealand have outbreaks during their winter (June-September) that could be spread here by air travel.

Flu vaccinations aren't yet recommended.