US flu activity continues to rise

US flu activity rose again last week, with the H3N2 strain expanding out of the southeast region, where it has been the dominant strain, and pushing into the south and central parts of the country, the Centers for Disease Control and Prevention (CDC) said today in its latest update.

The CDC said flu has reached a season high, with patterns similar to earlier seasons dominated by the 2009 H1N1 virus, according to an accompanying situation update. All of the CDC's regions have been above their flu baselines for 6 weeks in a row.

The CDC has said it expects flu levels to be elevated for the next several weeks, and it urges people to get vaccinated. It also reported more flu-related deaths in children.

More states report high, widespread flu

Overall, the percentage of clinic visits for influenza-like illness (ILI) rose to 4.8% last week, up from 4.3% the week before and remaining well above the national baseline of 2.2%.

Though the 2009 H1N1 strain has been predominant in most of the country except for the Southeast, the situation is starting to shift, and the CDC said south central states surrounding Texas and central states surrounding Kansas are now reporting equal proportions of 2009 H1N1 and H3N2.

The change has clinical implications, because H3N2 infections are especially tough on seniors and the youngest patients, and the virus typically poses more complex challenges for vaccine protection.

At clinical labs, the percentage of respiratory specimens that tested positive for flu rose from 22.8% to 24.6%, the highest point so far this season.

At the national level, of flu viruses tested last week at public health labs, 98.4% were influenza A and 1.6% were influenza B. Of the subtyped influenza A viruses, 64.5% were 2009 H1N1 and 35.5% were H3N2.

According to the CDC's flu maps, New York City and 26 states are experiencing high ILI activity, an indicator that tracks clinic visits for flu, an increase of 2 states from the previous week. And flu is now classified geographically as widespread in 48 states and Puerto Rico, 1 more state than the week before.

Hospitalizations, kids' deaths rise

The overall hospitalization rate rose to 23.8 per 100,000 population, up from 20.1 per 100,000 population. The levels are highest in seniors and children younger than 5 years old, but are still much lower than this point last season, which was severe.

Six more pediatric flu deaths were reported to the CDC last week, raising the season's total to 34. Of the latest fatalities, 2 were linked to 2009 H1N1 and occurred earlier this month and 4 were from unsubtyped influenza A viruses and occurred since Jan 26 and through the first part of February.

Meanwhile, the overall percentage of deaths from pneumonia and flu fell below the epidemic threshold of 7.3%.

See also:

Feb 15 CDC FluView report

Feb 15 CDC weekly flu situation report

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