Flu activity at low levels in US, worldwide

May 11, 2012 (CIDRAP News) – US influenza activity declined overall and in most regions last week, the Centers for Disease Control and Prevention (CDC) reported today, while Northern Hemisphere flu activity in general continued to fall.

Two states, Alabama and Hawaii, still had "low" influenza-like illness (ILI) activity, while the other 48 had minimal levels. The share of doctor visits for ILI ticked up slightly, to 1.4%, but remained well below the national baseline of 2.4%, while 6.9% of deaths were attributed to pneumonia and flu, below the epidemic threshold of 7.5%.

Flu was cited in the deaths of two children, raising the season's total of pediatric deaths to 22. The share of respiratory specimens that tested positive for flu was 13.7%, down from 15.3% the previous week.

Type A viruses made up 64.6% of the isolates, and of these, about 60% were H3N2 viruses, 13% were 2009 H1N1, and the rest were not subtyped.

In Europe, 22 of 23 reporting countries confirmed low-intensity flu activity last week, while Slovakia reported medium activity, the European Centre for Disease Prevention and Control (ECDC) said today. Cases were listed as declining in 12 countries and stable in 11.

Analysis showed growing evidence of an imperfect match between circulating H3N2 and B strains and the seasonal vaccine, which supports the World Health Organization (WHO) recommendation to change two of the three vaccine components for next season, the report says.

Internationally, the WHO said today that flu activity continued to decline in the Northern Hemisphere and was generally low worldwide in the second half of April (Apr 15-28).

H3N2 viruses were most common overall, but type B viruses were predominant in some countries, including Canada, Japan, and South Korea, while 2009 H1N1 viruses circulated at lower levels. India reported co-circulation of 2009 H1N1 and B viruses.

Flu activity remained low in the Southern Hemisphere, where most of the viruses detected were H3N2, the WHO said.

Of 5,297 flu viruses identified by national flu labs globally, 63.1% were A strains and 36.9% were B. Of A viruses that were subtyped, 86.6% were H3N2 and 13.4% were 2009 H1N1.

See also:

May 11 CDC flu update

May 11 ECDC update

May 11 WHO flu update

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