Mar 25, 2013 (CIDRAP News) – The nation's flu indicators continue to drop with the start of spring, but virus activity is still significant in many parts of the country, the US Centers for Disease Control and Prevention (CDC) said in its most recent surveillance report.
Though the percentage of respiratory samples that tested positive for flu rose slightly from 14.3% to 16.3% over the week that ended Mar 16, the percentage of clinic visits for flulike illness fell to its baseline level of 2.2%, the CDC said in its Mar 22 report.
Health officials saw the proportion of influenza B samples grow again to 72% of all positive flu samples reported, and 8 of the CDC's 10 regions reported more influenza B than influenza A.
Six more pediatric flu deaths were reported, boosting the number so far this season to 105. One was from the 2009 H1N1 virus and occurred nearly a month ago and the other five were from influenza B and occurred between late January and the middle of March.
Overall deaths from pneumonia and flu stayed steady at 7.6% compared with the previous week, which is just above the epidemic threshold.
Testing for resistance to neuraminidase inhibitors identified a second H3N2 virus sample that showed resistance to oseltamivir (Tamiflu).
Flu hospitalizations were up slightly again, rising from 39.6 per 100,000 population to 40.6 per 100,000, the CDC said. Seniors are still the group hardest hit by severe flu this season.
Elsewhere in North America, flu activity in Canada is at expected levels for this time of year, and, similar to in the United States, influenza B has increased in recent weeks and is now the dominant strain, according to a Mar 20 report from the Pan American Health Organization (PAHO). In Mexico, however, H3N2 is still the dominant strain.
Europe, which has also seen flu continue to cause substantial illness over the past several weeks, reported more signs of waning, according to a Mar 22 update from the European Centre for Disease Prevention and Control (ECDC). It said all countries except for one—Romania—are reporting that flu continues to decline or has already returned to baseline.
Overall, the percentage of respiratory specimens that tested positive for flu dropped to 46% compared with 54% the previous week, the ECDC said. Influenza B detections are slightly edging out influenza A identifications, and, of the subtyped influenza A samples, 63% are the 2009 H1N1 virus.
Mar 22 CDC weekly flu update
Mar 20 PAHO flu report
Mar 22 ECDC weekly surveillance report