U.S. influenza activity gradually increasing

ATLANTA For the week ending Jan. 17, influenza activity continued to slowly increase in the United States, the Centers for Disease Control and Prevention reported Friday.

Widespread influenza activity was reported in Virginia and six additional states — Colorado, New Hampshire, New Jersey, New York, North Carolina and Texas — reported regional activity (meaning widespread activity has been detected in at least two, but less than half, of the regions within the state). Localized activity was reported in 11 states; Washington, Puerto Rico and 30 states reported sporadic activity; while two states, Mississippi and Oklahoma, reported no activity.

CDC has antigenically characterized 207 influenza viruses — 142 influenza A (H1), 13 influenza A (H3) and 52 influenza B viruses — collected by U.S. laboratories since Oct. 1.

All 142 influenza A (H1) viruses are related to the influenza A (H1N1) component of the 2008-09 influenza vaccine (A/Brisbane/59/2007). All 13 influenza A (H3N2) viruses are related to the A (H3N2) vaccine component (A/Brisbane/10/2007).

Influenza B viruses currently circulating can be divided into two distinct lineages represented by the B/Yamagata/16/88 and B/Victoria/02/87 viruses. Seventeen influenza B viruses tested belong to the B/Yamagata lineage and are related to the vaccine strain (B/Florida/04/2006). The remaining 35 viruses belong to the B/Victoria lineage and are not related to the vaccine strain.

Since Oct. 1, 2008, 160 influenza A (H1N1), 30 influenza A (H3N2), and 66 influenza B viruses have been tested for resistance to the neuraminidase inhibitors Tamiflu and Relenza. In 25 states, at least one Tamiflu-resistant influenza A (H1N1) virus has been identified. To date, all influenza A (H3N2) viruses tested are resistant to adamantanes, an older class of antiviral drugs.