US flu activity continues to rise sharply

Jan 4, 2013 (CIDRAP News) – Influenza activity continued its sharp rise through the last week of 2012, the Centers for Disease Control and Prevention (CDC) said today.

"Reports of influenza-like-illness (ILI) are nearing what have been peak levels during moderately severe seasons," said Joe Bresee, MD, chief of epidemiology and prevention in the CDC's flu division, in a CDC statement today.

The percentage of outpatient visits for ILI reported to the CDC's ILI network reached 5.6% for the week ending Dec 29 (week 52), up from 4.2% the week before and well above the national baseline of 2.2%. In the last moderately severe flu season, 2007-08, ILI activity peaked at 6.4%, in late February.

By comparison, that marker reached 8.0% during the peak of the 2009 pandemic in October, according to CDC data.

As outlined in the agency's weekly FluView update, 31.6% of 9,363 lab-tested respiratory specimens during week 52 were positive for flu, up from 29.6% the week before. That number approached 60% in Midwestern states.

Forty-one states reported geographically widespread flu activity, seven had regional activity, and one reported sporadic activity. During the previous week, 31 states reported widespread flu activity.

The H3N2 strain—typically associated with more-severe seasons—continued to dominate, constituting 1,209 (98%) of 1,234 influenza A viruses that were subtyped, with the other 2% being pandemic 2009 H1N1. All told, 79% of flu viruses tested were type A and 21% type B.

The circulating strains continue to be well matched to the strains in the flu vaccine, and no resistance to antiviral drugs has been detected, the CDC said.

Two new pediatric flu deaths were reported, bringing the season total to 18.

"While we can't say for certain how severe this season will be, we can say that a lot of people are getting sick with influenza and we are getting reports of severe illness and hospitalizations," Bresee said, adding, "Anyone who has not already been vaccinated should do so now."

H1N1 more important in Europe
In Europe, increased flu activity is also being seen, with 2009 H1N1 more prevalent there than in the United States.

Five European countries reported widespread flu activity for the week ending Dec 29 (Belgium, Denmark, France, Norway, and the United Kingdom), compared with three the previous week, according to an update today from the European Centre for Disease Prevention and Control (ECDC). In addition, four countries are reporting medium-intense clinical activity.

Of 375 specimens tested from sentinel patients, 25.3% were positive for influenza, down slightly from the previous week's level of 27.3%. The drop, however, may be related to a lower number of physician consultations over the holidays, the ECDC said.

Since the start of the season, 46% of European specimens have been influenza A and 54% type B, the ECDC said, with the proportion of B viruses decreasing slightly in recent weeks. Of the A viruses, 56% have been the H3 strain and 44% H1. The viruses are well matched to the vaccine strains.

See also:

Jan 4 CDC flu statement

Jan 4 CDC FluView update

Jan 4 ECDC update

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