CDC says flu trends still rising

Mar 9, 2012 (CIDRAP News) – Flu activity in the United States continued its late-season rise last week, with more respiratory specimens testing positive and more states reporting widespread activity, but flu-like illness stayed relatively low overall, the US Centers for Disease Control and Prevention (CDC) said today.

Though doctor visits for flu-like illness stayed below the baseline, levels were above regional baselines for much of the Midwest, the agency reported.

The percentage of respiratory specimens that were positive for influenza climbed to 21.3%, compared to 18.4% the previous week.

The rate of hospitalizations for lab-confirmed flu reached 2.1 per 100,000 people last week, an increase of 36% from the previous week, though levels are still lower than expected for this time of the year, according to the CDC. Most (87.9%) of the hospitalizations this flu season have involved influenza A strains, and of 246 type A isolates that were subtyped, 185 were H3N2 and 61 were 2009 H1N1.

The percentage of deaths from flu and pneumonia rose slightly last week but is still below the epidemic threshold. The CDC received one more pediatric flu death report, raising the season's total so far to five. The child's death was linked to an H3N2 infection.

The H3N2 subtype is still predominant, especially in the upper and central Midwest regions, but the overall percentage of 2009 H1N1 viruses is increasing nationally and in several regions, according to the CDC.

Three states reported high flu-like illness activity: Kansas, Missouri, and Oklahoma. Nine states reported wide geographic spread of flu cases, an increase of three from the previous week. The states are California, Colorado, Illinois, Kansas, Missouri, Nevada, New Jersey, Oklahoma, and Virginia.

Elsewhere, flu activity in the European Union (EU) rose last week, though levels in some countries, including Bulgaria, Italy, and Spain, have already peaked, the European Centre for Disease Prevention and Control (ECDC) said today.

Overall in the EU, the percentage of specimens testing positive for flu showed a solid drop, the first real decline of the flu season, according to the ECDC's weekly report. Though H3N2 is still the dominant strain, the percentage of influenza B viruses is rising. Very few 2009 H1N1 viruses have been detected.

See also:

Mar 9 CDC flu surveillance report

Mar 9 ECDC flu surveillance report

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