US flu activity drops for second week

Lisa Schnirring
Influenza, General

Mar 21, 2011 (CIDRAP News) – For the second week in a row, most indicators of flu activity declined, except for deaths in children and overall deaths related to pneumonia and flu, the US Centers for Disease Control and Prevention (CDC) said in its most recent update.

The CDC said in its Mar 18 surveillance report that it received 11 more reports of pediatric flu deaths, raising the total for the season to 71. Four were linked to influenza B, 3 with the 2009 H1N1 virus, 2 to H3N2, and 2 to unsubtyped influenza A viruses. The percentage of deaths from flu and pneumonia rose slightly to 8.6%, up 0.1% from the previous week, keeping it above the national baseline for the seventh week in a row.

In the past the CDC has said that deaths can sometimes lag behind other flu indicators.

Overall, the CDC still characterized flu as widespread, with 31 states still reporting widespread activity, 8 fewer than the week before. Though the national percentage of doctor's visits for flu-like illness fell slightly, from 3.1% to 3.0%, 8 of the CDC's 10 regions are still reporting percentages above their baselines. Areas reporting normal levels of doctor's visits for flu were the mid-Atlantic states and the southern region, which includes states like Louisiana, Texas, and New Mexico.

The percentage of respiratory specimens that tested positive for influenza fell to 21.1%, down from 24.7% the week before, the CDC reported. All flu types and subtypes continued to circulate widely, with 27.1% of it influenza B. Of the influenza A viruses that were subtyped, 57% were H3N2 and 43% were 2009 H1N1.

Circulating viruses are still a good match to the ones in the seasonal flu vaccine, and overall they remain susceptible to the neuraminidase inhibitors oseltamivir (Tamiflu) and zanamivir (Relenza). Though identifications of oseltamivir-resistant 2009 H1N1 viruses in respiratory samples have been very rare this season, two more were found during the previous week, raising the total for the season to three.

See also:

Mar 18 CDC flu surveillance update

Mar 18 CDC flu situation update

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