CDC: Flu season stretches on with late H3N2 push

Senior female hospital patient
Senior female hospital patient

parinyabinsuk / iStock

The US flu season is already a long one, with illness activity still widespread in 44 states and expected to continue for several more weeks, the Centers for Disease Control and Prevention (CDC) said in its latest weekly update.

Though the level of clinic visits for flu peaked in February, the latest markers show little change from the previous week, with H3N2 viruses causing an increasing number of infections. Though 2009 H1N1 has been predominant for most of the season, H3N2 has caused more illnesses for 3 weeks in a row now.

The CDC said the most recent flu seasons have averaged 16 weeks above baseline for flulike illness, but so far this season, flu levels have topped baseline for 17 weeks. Also, the agency recorded eight new flu-related deaths in children.

H3N2 rise predicted to be tough on seniors

The CDC said it continues to recommend flu vaccination and antiviral drugs. In older adults, H3N2 typically causes more severe illness than in other age-groups, and in seniors, the vaccine doesn't protect as well against H3N2, the CDC warned.

"Prompt treatment with flu antivirals in this age group especially important during the current period of A(H3) predominance," it said in its summary of the weekly FluView report.

Nationally, the percentage of respiratory specimens testing positive for flu at clinical labs for the week ending Mar 16 was 26%, slightly up from 25.1% the week before. Of specimens tested, 96.4% were influenza A and 3.6% were influenza B.

At public health labs, of the subtyped influenza A viruses, 65.4% were H3N2 and 34.6% were 2009 H1N1.

Another key marker—percentage of clinic visits for flulike illness—was at 4.4%, still well above the national baseline of 2.2% and down only a bit from the previous week's 4.5%. Twenty-six states are still reporting high flu activity, another measure of clinic visits for flu.

Geographically, flu is still widespread in 44 states,  down slightly from 46 and Puerto Rico reported the previous week.

Pediatric flu deaths rise to 76

The hospitalization rate for flu continues to rise and was at 47.1 per 100,000 population in the most recent reporting week, up from 41.3 per 100,000 population the week before. Highest rates are in adults age 65 and older, followed by adults ages 50 to 64 and children younger than 5.

Eight more deaths from flu in children were reported, bringing the season's total to 76. Two were related to 2009 H1N1, two from H3N2, three from unsubtyped influenza A, and one due to influenza B. The previous three flu seasons saw 95, 110, and 185 pediatric flu deaths over the entire season, respectively, according to CDC data.

Overall deaths from pneumonia and flu was 7.1%, which is below the epidemic threshold of 7.3%.

See also:

Mar 22 CDC FluView

Mar 22 CDC situation update

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