CDC gives mixed report on US flu activity

Jan 7, 2011 (CIDRAP News) – US health officials today gave a mixed report on influenza activity for last week, saying overall activity decreased slightly but more states reported widespread flu than the week before.

In Europe, meanwhile, flu activity increased in several countries, and the United Kingdom and Denmark reported high flu circulation, according to the World Health Organization's (WHO's) European Regional Office.

In the United States, influenza-like illness (ILI) accounted for 2.6% of outpatient visits to sentinel healthcare providers in the week that ended Jan 1, down from 2.7% the week before but still above the national baseline of 2.5%, the US Centers for Disease Control and Prevention (CDC) reported in its weekly update. The CDC said the holidays might have reduced the number of routine medical visits last week, possibly making the proportion that were ILI-related higher than it would have been otherwise.

Eight states—Alabama, Arizona, Georgia, Kentucky, Louisiana, New York, North Carolina, and Virginia—reported geographically widespread flu activity, up from five states the week before, according to the CDC. Sixteen states and Puerto Rico reported regional flu activity, while the rest had only local or sporadic flu circulation

State reports on ILI activity differed slightly from the state reports on the geographic extent of flu outbreaks. New York City and six states—Alabama, Georgia, Illinois, Louisiana, Mississippi, and Oklahoma—reported high ILI activity, meaning much above the average level of ILI visits for weeks when flu circulation is low. Nevada and New Jersey both reported moderate ILI activity, and the rest reported either low or minimal activity.

The CDC also said the proportion of deaths attributed to pneumonia and flu was below the epidemic threshold. Only one flu-related pediatric death was reported, with influenza B as the cause.

Of 4,911 respiratory specimens tested and reported to the CDC last week, 20.3% were positive for flu, compared with 21.0% the previous week. Of the 995 positive samples, 656 (65.9%) were type A and 339 (34.1%) were type B. Labs subtyped 313 of the influenza A isolates and found that 269 (86%) were H3N2 and 44 (14%) were 2009 H1N1.

The CDC said antigenic characterization of a sample of the isolates continued to show that they overwhelmingly matched the strains in this year's flu vaccine. Also, the CDC reported it has found no isolates resistant to oseltamivir or zanamivir so far this season, though the CDC data do not include diagnostic testing in cases of suspected resistance.

In Europe—where the United Kingdom's flu epidemic has been in the spotlight lately—12 of 32 reporting countries cited increased medical consultations for ILI or acute respiratory infection last week, according to the WHO's EuroFlu Weekly Electronic Bulletin. Most of the cases were in children under age 5, the WHO said.

England and Denmark reported "high intensity" flu circulation, the agency said. Of 10 countries that estimate baseline levels of flu, 5—France, Ireland, Israel, Luxembourg, and Ukraine—said activity exceeded the baseline.

However, only 11 of 38 countries that report on the geographic extent of flu circulation said they had widespread activity. Most of those countries are in Western Europe: Belgium, Denmark, Ireland, Israel, France, the Netherlands, Norway, Portugal, Switzerland, and the UK (England and Wales). Five countries cited regional activity, 6 reported local activity, and the other 16 had only sporadic activity or none.

Unlike in the United States, most of the influenza A isolates in Europe so far have been 2009 H1N1, the WHO said. Out of 479 flu isolates, 77% were type A and 23% were type B. Labs reported that of 307 type A isolates that were subtyped, 85% were H1N1 and 15% were H3N2.

In Japan, flu cases have increased for 10 straight weeks, and there were 9,863 flu patients during the week that ended Dec 26, according to a report from the Japan Broadcasting Corp. today.

Japan's National Institute of Infectious Diseases said 62% of cases in December were due to the 2009 H1N1 virus, though other strains had predominated earlier in the season, according to the story.

See also:

Jan 7 CDC flu update

WHO EuroFlu Weekly Electronic Bulletin

Jan 7 Japan report

Dec 30 CIDRAP News story "Flu activity up globally, in US, and notably in UK"

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