Jan 6, 2012 (CIDRAP News) – Though flu activity is still below epidemic thresholds in most of the Northern Hemisphere, increases in areas such as Spain, northern Africa, and part of Canada suggest that the season is starting, the World Health Organization (WHO) said today.
Meanwhile, most flu markers in the United States showed low levels of activity, but three regions saw the percentage of doctor's visits for flu-like illness rise above their baselines, according to the US Centers for Disease Control and Prevention (CDC).
So far H3N2 is the dominant influenza strain in the Northern Hemisphere, with small numbers of 2009 H1N1 cases reported over the past few weeks, the WHO said.
In most of Europe, flu activity remained at interseasonal levels, but Spain and Turkey reported notable increases in flu virus detections, according to the WHO. The number of positive respiratory samples at European sentinel sites doubled from the previous week.
The European Centre for Disease Prevention and Control (ECDC) in its weekly update today said the flu season has begun in Europe. Though the H3N2 virus is dominant so far, making up about 94% of the viruses that have been subtyped, the 2009 H1N1 virus "features significantly" in the severe flu infections that have been reported so far.
The percentage of respiratory specimens testing positive for flu more than doubled from the previous week, rising from 9.3% to 23.4%, the ECDC said.
Most countries reported low-intensity flu activity, with the Netherlands, Norway, and Spain reporting local spread, according to the ECDC. Nine countries and the United Kingdom reported sporadic activity.
So far all viruses that have been tested for antiviral resistance were sensitive to neuraminidase inhibitors, the ECDC said.
In a virus characterization report today, Europe's influenza lab network said the H3N2 viruses collected since February 2011 fall into seven distinct genetic categories, but that the most recently collected isolates are within group 3 and have evidence of altered antigenicity when compared to the vaccine strain. The ECDC said in background information that the match between the circulating strains and the vaccine is "reasonable."
The WHO said countries in northern Africa and the eastern Mediterranean region, including Algeria, Tunisia, and Iran, have reported increasing levels of flu activity since October. In temperate parts of Asia, flu levels rose slightly in countries such as China, where influenza B is predominant.
In tropical locations, flu activity remained low except for Costa Rica, which has reported increasing numbers of H3N2 detections, the WHO reported.
Some parts of Canada, such as British Columbia, flu levels have persistently increased since the middle of December, though as a whole, flu indicators are still at interseasonal levels, the WHO said.
The CDC reported that US flu activity increased last week, but levels were still low. Overall, the percentage of doctor's visits for flu-like illness remained below the national baseline, but the level rose above regional baselines for the first time this season in three areas: the Northeast, the Midwest, and the Northwest.
However, the percentage of deaths from pneumonia and flu dropped slightly and remained below the epidemic threshold, and the CDC received no reports of pediatric flu deaths.
Of the flu viruses collected last week, 47% were H3N2, about 10% were influenza B; and 43% were unsubtyped. No novel flu infections were reported.
No states reported widespread flu activity, and only one state—Colorado—reported regional spread.
Jan 6 WHO global flu update
Jan 6 CDC flu update
Jan 6 ECDC flu update
Jan 6 ECDC flu virus characterization report