Flu activity gaining steadily in US, Europe

Feb 10, 2012 (CIDRAP News) – Seasonal flu activity in the United States last week passed a key threshold, while many European countries reported similar rises in the spread of the disease, according to flu surveillance reports released today.

The US Centers for Disease Control and Prevention (CDC) said the percentage of respiratory specimens that tested positive for flu jumped from 7.6% to 10.5%, passing a mark (10%) that health officials typically use to gauge when the season has started. It also reported that California became the first state to cite widespread flu transmission this year.

Alhough the nation's rise in flu activity seems late this year, the CDC has said that in the past 29 years, specimens testing positive for flu didn't pass the 10% mark until January or later in 15 of the years.

Nationally, the percentage of doctor visits for flu-like illness was 1.7%, putting it below the baseline. However, regional baselines were exceeded in two parts of the country: Iowa, Kansas, Missouri, and Nebraska; and the northwest, including Alaska, Idaho, Oregon, and Washington.

Deaths from flu and pneumonia were below the epidemic threshold, the CDC said. One more pediatric flu death was reported, raising the season's total to two. The child's death occurred during the week that ended Jan 21 and involved an unsubtyped influenza A strain.

Although H3N2 viruses are still dominant, the CDC is seeing regional differences in circulating viruses, including a rising number of 2009 H1N1 detections over the past several weeks, especially in south-central and southwestern states.

Antigenic testing of a small number of influenza B samples shows that fewer than half (45.9%) match the Victoria lineage included in the seasonal flu vaccine. However, the CDC said it is too soon to tell how well circulating strains match the vaccine strains and that most influenza B strains circulating globally match the vaccine strain.

The 2009 H1N1 virus has dominated Mexico's flu season. The Pan American Health Organization (PAHO) said Mexico has reported 2,815 influenza infections and 58 deaths, with about 90% of the cases and 93% of the deaths due to the 2009 H1N1 virus. States with the most cases are Federal District and Oaxaca.

Meanwhile, the European Centre for Disease Prevention and Control (ECDC) said today that flu activity continued to rise last week with significant variation by country and no clear geographic progression. Belgium, Italy, and Spain reported widespread activity, and 18 countries reported increasing activity.

The ECDC said the H3N2 virus is dominant, with low levels of influenza B and 2009 H1N1 circulating as well. So far no resistance to neuraminidase inhibitors has been reported.

See also:

Feb 10 CDC influenza update

Feb 7 PAHO report

Feb 10 ECDC influenza update

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