Nationally, flu markers that the CDC uses to track activity are still below their baselines, but for two regions, the percentage of clinic visits for flu like illness have reached their baselines. One is in the southwest in a region that includes Arkansas, Louisiana, New Mexico, Oklahoma, and Texas. The other is in the central part of the country in a region that includes Iowa, Kansas, Missouri, and Nebraska.
[Note the baseline is developed by calculating the mean percentage of patient visits for ILI (Influenza Like Illness) during non-influenza weeks for the previous three seasons and adding two standard deviations.]
However, the agency added that all three strains are circulating, with patterns that vary by region and patient age. At public health laboratories last week, 59% of specimens that tested positive for flu were influenza B and 41% were influenza A. And of the sub typed influenza A viruses, 61.5% were 2009 H1N1 and 38.5% were H3N2.
Influenza B was most common in people younger than 24 years old and H3N2 was most common in seniors. In adults ages 24 to 64, equal proportions of all three strains have been reported.
Regional patterns show that influenza B is more common in the south and southeast, 2009 H1N1 is more frequently detected in the central states, and H3N2 is more common in the northeast.
The CDC report for Week 47 is due out ant time now.