WHO report sums up Northern Hemisphere flu season

Jun 15, 2012 (CIDRAP News) – The 2011-12 flu season in most temperate countries of the Northern Hemisphere started later than usual, except for North Africa, and was mild in many countries, the World Health Organization (WHO) said today in a wrap-up report.

The circulating flu strains varied widely by country and even by region, according to WHO report, which appeared in its Weekly Epidemiological Record. For example, in North America, the 2009 H1N1 virus predominated in Mexico, with H3N2 dominating in the United States, and influenza B taking the lead in most parts of Canada.

In temperate parts of Asia, influenza B peaked first in China and Mongolia, followed by a rise in H3N2 activity later in the season. The reverse pattern was seen in South Korea and Japan.

Many countries saw doctors' visits for flulike illness at or below last season's levels, but Japan reported its highest number of confirmed flu cases since 2002, except for during the 2009 pandemic period, the WHO report said.

Some European countries such as Spain and France reported excess mortality in older adults, much of it related to H3N2 that circulated in those areas. European officials also reported that the 2009 H1N1 virus was overrepresented in cases of severe influenza.

As the season progressed, influenza lab experts noted drift in the H3N2 strain and increasing numbers of influenza B samples from the Yamagata lineage, which prompted WHO advisors to recommend changing two of the three strains for the Northern Hemisphere's 2012-13 flu season.

Little oseltamivir (Tamiflu) resistance was seen in 2009 H1N1 viruses, except for 16 cases from Texas late in the flu season. Among 14 cases with available information, 3 patients had taken the drug for 1 day or more at the time of specimen collection, and 2 had family members taking the oseltamivir. Nine had no oseltamivir exposure.

In the United States last week, flu markers remained well below baselines, with no new pediatric flu deaths reported, the US Centers for Disease Control and Prevention (CDC) said in an abbreviated form of its weekly flu update.

In other flu developments, Bermuda's health department is reporting an unusual spike in flu illnesses, the Royal Gazette reported on Jun 13. A spokeswoman for the Bermuda Hospitals Board said 26 patients with flulike illness were hospitalized between Jun 6 and Jun 13, a level higher than expected at this time of the year. She added that the hospitalization pattern is probably accompanied by a wave of cases reported to doctors' offices.

See also:

Jun 15 Wkly Epidemiol Rec report

Jun 15 CDC weekly influenza update

Jun 13 Royal Gazette story

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