CDC: Flu prevalence remains high

ATLANTA — According to this week's FluView report, overall flu activity continued to be high across the nation, with activity continuing to spread from state to state, the Centers for Disease Control and Prevention reported Friday. Thirty-five states are now experiencing widespread activity, and 20 states are reporting high levels of influenza-like illness. 

For the week ended Jan. 4, the proportion of people seeing their healthcare provider for ILI decreased, but remains above the national baseline. "The apparent decrease this week is likely due to differences in care-seeking, testing and reporting practices over the holidays, rather than an actual decline in flu activity," the CDC noted.  

Twenty states experienced high ILI activity, the same number as in the previous week. Seven states and New York City experienced moderate ILI activity, while 11 states experienced low ILI activity, and 12 states experienced minimal ILI activity.  

To date, influenza A (H1N1) viruses have predominated. This is the same H1N1 virus that emerged in 2009 to cause a pandemic, CDC noted. H1N1 viruses have continued to circulate among people since that time, but this is the first season that the virus has circulated at high levels since the pandemic. 

The predominant flu strains in circulation are well matched to the Northern Hemisphere quadrivalent and trivalent vaccines for the 2013-2014 season.

The neuraminidase inhibitors Tamiflu (oseltamivir) and Relenza (zanamivir) are currently the only recommended influenza antiviral drugs. While the vast majority of the viruses that have been tested are sensitive to oseltamivir and zanamivir, three additional 2009 H1N1 viruses proved resistant to oseltamivir during the week ended Jan. 4. So far this season 13 (1.2%) 2009 H1N1 viruses have shown resistance to oseltamivir. No viruses have shown resistance to zanamivir.

As in recent past seasons, high levels of resistance to the adamantanes (Symmetrel (amantadine) and Flumadine (rimantadine)) continue to persist among 2009 H1N1 and influenza A (H3N2) viruses. Adamantanes are not effective against influenza B viruses. Adamantanes are not recommended for use against influenza this season, the CDC noted.