Flu continues slow decline in US

Influenza A viruses
Influenza A viruses

Highly magnified influenza A viruses. Influenza A continues to greatly dominate influenza B in the US, Canada, and Europe., CDC / F. A. Murphy

Barometers of US influenza activity continued to reflect a slow decline last week, with no states reporting high activity, but the disease remained widespread in 17 states, the Centers for Disease Control and Prevention (CDC) reported today.

Last week was the first week since early November that no states reported high activity, according to CDC data. Six states were still reporting high activity the week before. Seven states cited moderate activity last week, with the rest reporting low or minimal numbers of cases.

The 17 states that still had geographically widespread cases were mostly in the Northeast but also included California and Arizona. A week earlier, 24 states were citing widespread activity.

Other markers were down last week as well, according to the CDC. The agency said 13.9% of 6,887 respiratory specimens tested positive for flu, compared with 16.8% of 7,562 specimens the previous week.

The share of medical visits ascribed to influenza-like illness (ILI) dropped to 2.5% last week from 3.0% a week earlier, but it stayed well above the national baseline of 2.0%.

The proportion of deaths attributed to pneumonia and influenza was 8.2%, which was above the epidemic threshold of 7.4% but down from 8.6% the week before.

The CDC reported two more flu-related deaths in children, raising the season's total to 52. One of the cases involved the 2009 H1N1 virus, while the virus in the other case was not subtyped.

The cumulative rate of flu-related hospitalizations this season reached 26.1 per 100,000 population, as the CDC's flu hospitalization surveillance network picked up another 418 cases, raising the total to 7,073. The network covers about 8.5% of the US population.

Only 26 flu isolates with resistance to neuraminidase inhibitors have been identified this season, including one last week. All of them have been H1N1 viruses.

Yesterday the CDC said elevated flu activity is expected to continue for several more weeks and urged people to get a flu shot if they haven't had one yet. With the 2009 H1N1 virus accounting for more than 90% of cases, the season has been worse than usual for young and middle-aged adults, who, early assessments suggest, have accounted for about 60% of hospital cases and deaths.

Activity down in Canada, mixed in Europe

In Canada, as in the United States, overall flu activity continued to decrease last week, the Public Health Agency of Canada (PHAC) said in its update today. But some of the eastern provinces didn't conform with that trend because the season started later there.

The H1N1 virus remains the predominant one in Canada, though detections of type B viruses are continuing to increase, the PHAC said. A total of 2,951 hospitalizations have been reported for the season so far, which is slightly fewer than in the same period last season. The death toll so far is 155, similar to the number at this time last year.

The flu picture in Europe, meanwhile, is mixed, the European Centre for Disease Prevention and Control (ECDC) noted today.

Among 29 reporting countries, two (Finland and Greece) are reporting high-intensity activity, the agency said. Another 11 countries report medium activity, while the other 16 have low numbers.

Activity is declining in some countries, but 18 countries and the United Kingdom reported increases, while 16 countries have geographically widespread cases, the ECDC said. The share of sentinel respiratory specimens testing positive for flu remained high, at 37%.

The agency said H1N1 and H3N2 viruses are both circulating in outpatient settings in Europe, but H1N1 is dominant in hospital cases, while few type B viruses have been detected.

See also:

Feb 21 CDC FluView report

Feb 21 PHAC update

Feb 21 ECDC report

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