U.S. health officials troubled by new flu pattern

WASHINGTON, 20 may 2009-- The new influenza strain circulating around most of the United States is putting a worrying number of young adults and children into the hospital and hitting more schools than usual, U.S. health officials said on Monday.

The H1N1 swine flu virus killed a vice principal at a New York City school over the weekend and has spread to 48 states. While it appears to be mild, it is affecting a disproportionate number of children, teenagers and young adults.

This includes people needing hospitalization -- now up to 200, said Dr. Anne Schuchat of the U.S. Centers for Disease Control and Prevention.

"That's very unusual, to have so many people under 20 to require hospitalization, and some of them in (intensive care units)," Schuchat told reporters in a telephone briefing.

"We are now experiencing levels of influenza-like illness that are higher than usual for this time of year," Schuchat added. "We are also seeing outbreaks in schools, which is extremely unusual for this time of year."

New York City Health Commissioner Dr. Thomas Frieden agreed with Schuchat.

"We're seeing increasing numbers of people going to emergency departments saying they have fever and flu, particularly young people in the 5 to 17 age group, " Frieden, who has been named by U.S. President Barack Obama as the new CDC director, told a news conference.

About half of all cases of influenza are being diagnosed as the new H1N1 strain, while the rest are influenza B, or the seasonal H1N1 and H3N2 strains. Flu season in the United States is usually almost over by May.

CDC officials say around 100,000 people are likely infected with the new flu strain in the United States and Schuchat said the 5,123 confirmed and probable cases and six deaths in the United States were "the tip of the iceberg."

MORE ILLNESS OVERALL

"We are seeing more reports of influenza-like illness from outpatient visits that we monitor than is typical for this time of year," Schuchat said.

Because doctors usually treat symptoms and only occasionally give flu tests to patients, the CDC must monitor reports of symptoms such as fever, cough and muscle aches to track flu activity. Some centers are doing actual influenza tests to confirm the patterns that are seen.

Influenza is a factor in 36,000 deaths a year in the United States and 250,000 to 500,000 deaths globally, the CDC says.

"Unlike the seasonal flu, we are seeing relatively few cases or hospitalizations in people over 65," Schuchat said. Usually flu kills the elderly and people with chronic diseases.

There is no evidence that a second, bacterial infection is worsening the H1N1 cases, Schuchat said.

When family members are questioned, it seems clear that children and teens are more prone to infection than older adults, Schuchat said. "People under 18 are more likely to have infections when another person in the family is infected," she said.

"One of our working hypotheses is that older adults may have some pre-existing protection against this virus due to their exposure long ago to some virus that may be distantly related," Schuchat said.

An alternative hypothesis is that it just has not had a chance to make its way into the older population yet.

(Editing by Julie Steenhuysen and Xavier Briand)