CDC: Flu activity continues to slow

Feb 15, 2013 (CIDRAP News) – The nation's flu markers show that the flu has probably peaked, though many states are still reporting plenty of infections and hospitalizations, the US Centers for Disease Control and Prevention (CDC) said today.

Though the percentage of doctors' visits for influenza-like illness (ILI) is still above baselines in all regions of the country, the overall national level fell from 3.6% to 3.2% last week, according to the CDC.

The drop was even steeper for another indicator, the percentage of respiratory specimens testing positive for flu, which fell from 23.3% to 19.7%. Nationally, the dominant strain is still H3N2, followed by influenza B.

Five pediatric flu deaths were reported, one from an undetermined influenza A subtype and four from influenza B. The deaths occurred over a range of weeks between Dec 29 and Jan 26. The new reports push the number of flu deaths in children so far this season to 64.

Overall deaths from pneumonia and flu are still running well above the epidemic threshold and rose slightly last week, from 9.0% to 9.1%.

The rate of flu hospitalizations also rose last week, from 29.8 to 32.1 per 100,000 population. The hardest hit group is still seniors, who account for more than 50% of reported hospital cases.

Seven fewer states last week reported widespread geographic spread of flu, putting that number at 31.

Lab testing of isolates for antiviral resistance found one more sample that showed resistance to oseltamivir, raising the number so far this season to two, the CDC reported. Both were 2009 H1N1 viruses.

Elsewhere in North America, ILI activity increased in Canada, but the spike is due to an increase in respiratory syncytial virus (RSV), with influenza levels remaining stable, according to a Feb 13 surveillance update from the Pan American Health Organization (PAHO). The group noted that RSV levels are also increasing in the United States.

H3N2 is the most commonly detected virus in Canada, Mexico, and the United States, according to PAHO.

Flu activity in Europe is still substantial, although a few countries have already reported peaks, according to the latest update from the European Centre for Disease Prevention and Control (ECDC). The percentage of respiratory samples that tested positive for flu dropped slightly last week, from 55% to 53%.

Germany, Luxembourg, and Sweden reported high-intensity transmission, with Belgium reporting very high intensity, according to the ECDC.

The agency said the proportion of influenza A and B samples continues a fairly even split, though the percentage of H1N1 detections continues to increase.

In a virologic update today, the World Health Organization (WHO) said H3N2 is the dominant strain in Asia and that flu activity remains high in China and Japan. In Hong Kong, increasing detections of both H3N2 and H1N1 were reported, signaling the start of its flu season, according to the WHO report, which also noted increased activity in Mongolia.

See also:

Feb 15 CDC influenza update

Feb 15 CDC flu situation update

Feb 13 PAHO flu situation report

Feb 15 ECDC report

Feb 15 WHO flu virus activity report

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