US flu activity edges higher

Robert Roos  News Editor

Feb 25, 2011 (CIDRAP News) – Influenza activity edged upward in the United States last week, with more states reporting widespread cases and more clinic visits attributed to influenza-like illness (ILI), the Centers for Disease Control and Prevention (CDC) reported.

Forty-four states reported widespread flu activity in the week that ended Feb 19, compared with 37 states the week before. Four states had regional activity, versus 10 a week earlier.

The CDC said 4.9% of visits to sentinel medical providers were due to ILI, up from 4.5% the week before and well above the national baseline of 2.5%.

On the basis of ILI visits to providers, 21 states had high ILI activity last week, compared with 20 the week before. Six states had moderate activity, versus nine the week before.

Six flu-related deaths in children were reported, compared with five a week earlier. Three of the victims had influenza B, while one each had H3N2 and 2009 H1N1 infections, and one case was not subtyped. Forty-one pediatric deaths have been reported so far this season, the CDC said.

One example of increased flu activity came from Grand Rapids, Mich., where a physician with Spectrum Health Medical Group reported a "significant upswing" in flu cases, according to a story yesterday from the Grand Rapids Press.

Dr. David Dobbie, chief of medical specialties with the group, said 15 flu patients had been admitted to Spectrum's intensive care unit (ICU), many were put on ventilators, and several required extracorporeal membrane oxygenation (artificial lung machines), according to the story. Almost all of the ICU patients had the 2009 H1N1 virus, Dobbie said.

The CDC report said 8.3% of deaths reported last week were ascribed to pneumonia and influenza, down from 8.9% the week before. The proportion remained above the epidemic threshold of 8.0% for the fourth straight week.

The agency said 31.3% of 9,154 respiratory specimens tested last week were positive for flu, a bit lower than the 35% the previous week. Of the positive samples, 33.9% were H3N2 viruses, 26.3% were 2009 H1N1, 22.4% were type B, and 39.7% were not subtyped. Those percentages showed little change from the week before. For the season overall, H3N2 has been the most common flu strain in the United States, with type B second and H1N1 third.

See also:

Feb 25 CDC flu update
http://www.cdc.gov/flu/weekly/?source=govdelivery

Feb 24 Grand Rapids Press report
http://www.mlive.com/health/index.ssf/2011/02/flu_upswing_reported_at_grand.html

Feb 18 CDC flu update
http://www.cdc.gov/flu/weekly/weeklyarchives2010-2011/weekly06.htm