Nov 16, 2012 (CIDRAP News) – Influenza activity showed almost no sign of picking up steam in the United States last week, the Centers for Disease Control and Prevention (CDC) said today.
Only 1.2% of outpatient visits to sentinel medical providers last week were attributed to flu, which is well below the national baseline of 2.2%, the CDC said in its weekly update. One state, Louisiana, reported moderate flu activity, but the rest of the states cited minimal or low activity.
No flu-related pediatric deaths were reported, and the share of deaths attributed to pneumonia and flu was 6.4%, just below the epidemic threshold of 6.5%, the CDC said.
From the geographic standpoint, the spread of flu was listed as regional in four states, local in eight, sporadic in 32 states and Washington, DC, and absent in five states.
Of 4,147 respiratory specimens tested in CDC-affiliated labs, 7.5% (311) were positive for flu, the agency said. Fifty-six percent of these were influenza A viruses, and 44% were influenza B. Among type A viruses, 46% were H3N2 strains, 1% were 2009 H1N1, and the rest were not subtyped.
Most of the isolates that have been antigenically characterized this season have been well matched to this year's vaccine, the CDC said. However, 11 of 35 type B viruses have been of the Victoria lineage, which is not in the vaccine.
The quiet US situation was matched in Europe. The European Centre for Disease Prevention and Control (ECDC) said all 27 countries that reported clinical data cited low-intensity flu activity, and most reported no geographic spread. No one was hospitalized with confirmed flu.
Of 386 sentinel respiratory specimens that were tested, 13 (3.4%) were positive for flu, including 9 type A and 4 type B isolates, the ECDC reported.
Five countries cited some indications of increases in flu-like illness, but "there is no suggestion that substantial influenza transmission has begun in any European country as yet," the ECDC said. "The rising rates in five countries are likely to be explained by other respiratory viruses."
Concerning the global picture, the latest flu update from the World Health Organization (WHO), issued Nov 12, described much the same situation as did the US and European reports. The agency said increased sporadic flu cases were reported in the Northern Hemisphere, while activity stayed low in the Southern Hemisphere. The report, however, covered weeks 42 and 43, two weeks earlier than the period covered by the CDC and ECDC updates.
H3N2 viruses were the predominant subtype globally, followed by type B and H1N1 viruses, the WHO reported.
CDC FluView report
Nov 16 ECDC report
Nov 12 WHO update