Dec 28, 2012 (CIDRAP News) – US influenza activity continued its ascent last week, judging from the high volumes of patients seeking care for the disease at doctors' offices, while flu indicators in Europe showed a clear spike, according to the latest surveillance reports.
Outpatient clinic visits for influenza-like illness (ILI) in the United States rose to 4.2% of all visits, well above the national baseline of 2.2%, according to the weekly report from the Centers for Disease Control and Prevention (CDC).
High levels of ILI activity were reported in 16 states and New York City, an increase from 12 states the previous week, the CDC said. The only area that wasn't over its baseline for this flu marker was the western region, which includes Arizona, California, Guam, Hawaii, and Nevada.
The US flu season started early this year, and health officials have said they expect a bad year, because the dominant flu strain is H3N2, which tends to cause more severe illnesses. In some hard-hit areas, such as parts of North Carolina, hospitals are limiting visitors to curb the spread of flu to high-risk patients.
Eight pediatric flu deaths were reported last week, pushing the season's total to 16. Three were linked to influenza B viruses, three were associated with H3N2, and the influenza A subtype wasn't determined for the other two. The percentage of deaths from pneumonia and flu remained below the epidemic threshold, but this indicator usually lags other flu markers.
The percentage of respiratory specimens testing positive for flu stayed high at 29.6%, up from 28.3% reported the week before, according to the CDC.
Labs that monitor the circulating flu strains report that H3N2 is still the dominant strain, followed by influenza B.
Few 2009 H1N1 viruses have been detected in the United States, but the virologic picture in Europe is different, with the virus accounting for close to a third of influenza A viruses that have been subtyped.