US indicators show flu activity increasing

Jan 21, 2011 (CIDRAP News) – Flu in the United States picked up last week, increasing its geographic impact and sending more people to doctors' offices, the US Centers for Disease Control and Prevention (CDC) said today.

The rise in activity comes after 2 weeks of slight declines in some indicators, during which the CDC warned that flu activity had not likely peaked yet. Such rises and falls aren't unusual, and flu activity in the United States typically peaks in January or later, it said today in a surveillance update.

Meanwhile, British officials said yesterday that flu levels are declining in the United Kingdom, with the number of doctor's visits declining for the third consecutive week, according to an update from the Health Protection Agency (HPA).

In the United States, flu activity in two more regions, which include six northeastern and six Midwestern states, pushed above their baselines, as the level stayed elevated again in the region that includes eight southeastern states.

Seventeen states reported widespread flu activity, up from 11 the previous week. States reporting regional activity dropped from 17 to 15.

Doctor's visits for flu-like illnesses rose slightly above the national baseline of 2.5% after dipping below it the previous week.

The percentages of respiratory samples that tested positive for flu also rose, to 25.9%, which is up from 16.3% the week before.

Deaths from pneumonia and flu stayed below the epidemic threshold, according to the CDC's report. Two more pediatric flu deaths were reported, one from an influenza A (H3) virus and one from an influenza A virus that wasn't subtyped, raising the total for the season to 10.

Of the respiratory specimens that tested positive for flu, nearly 85% were influenza A. Though most of the influenza A samples were H3N2, the percentage of 2009 H1N1 viruses doubled from the previous week, to nearly 16%. More of the viruses were subtyped, though, compared with the previous week. About 15% of samples yielded influenza B, down from about 26% the week before.

British health officials said doctor's visits for flu-like illness fell to 66.5 per 100,000 people last week, down sharply from 108.4 per 100,000 the week before. The levels had declined over the previous 2 weeks, but health officials were cautious and warned that they could be down due to some offices being closed during the holiday period.

The HPA reported 142 more flu deaths, but said a substantial number of them occurred over the past 6 weeks and because of a holiday backlog were just confirmed. Since Britain's season started in October, 254 deaths have been reported.

The predominant UK strains are still 2009 H1N1 and influenza B viruses. The HPA said a small proportion of severe infections are still occurring, especially in people younger than 65.

In cases for which information is available, 81% of the patients who died from flu were in groups that put them at high risk for complications.

Ongoing surveillance continues to suggest a modest increase in some invasive bacterial infections, such as pneumococcal and meningococcal disease, according to the HPA. "Although we expect to see more cases of these bacterial infections during the winter months, the HPA is monitoring the situation closely and currently investigating whether co-infection with flu is contributing to these increases," he said.

See also:

Jan 21 CDC flu update summary

Jan 21 CDC FluView

Jan 20 HPA report

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