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CDC: I221V Mutation ID'd in North Carolina Influenza B Virus

Cluster of viruses identified in North Carolina have increased oseltamivir resistance

WEDNESDAY, Oct. 5 (HealthDay News) -- Influenza B viruses carrying the I221V mutation, which have reduced susceptibility to oseltamivir, have been identified in North Carolina, according to a study published in the November issue of the U.S. Centers for Disease Control and Prevention's Emerging Infectious Diseases.

Katrina Sleeman, Ph.D., from the CDC in Atlanta, and colleagues described and characterized a cluster of influenza B viruses circulating in North Carolina, with a mutation in the neuraminidase active (NA) site. Fluorescent neuraminidase inhibition testing of isolates was performed, followed by pyrosequencing analysis. A total of 258 influenza B isolates submitted to the CDC for routine analysis were screened for the I221V mutation. Enhanced surveillance and epidemiologic investigation was carried out for 220 patients with influenza B virus infections in North Carolina during November 2010 through March 2011. Pyrosequencing was carried out in 209 patients, and antiviral treatment information was available for 199 patients.

The investigators found that testing of isolates recovered during surveillance identified a cluster of 14 influenza B viruses from North Carolina with increased oseltamivir and peramivir resistance. Based on results from the North Carolina patients, the I221V mutation was the most common NA mutation, present in 22 percent of patients. None of the patients with antiviral treatment information had documented exposure to the virus before specimen collection. Based on phylogenetic analysis of the hemagglutinin gene of the North Carolina B viruses with I221V mutation, this change was consistent with the B Victoria lineage.

"The clinical significance of the altered susceptibility [to oseltamivir] associated with I221V in influenza B viruses is unknown at this time and warrants further investigation," the authors write.

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