A cluster of patients infected with I221V influenza b virus variants with reduced oseltamivir susceptibility--North Carolina and South Carolina, 2010-2011.

BACKGROUND: During 2010-2011, influenza B viruses with a novel neuraminidase substitution, denoted I221V (B/I221V), associated with reduced in vitro oseltamivir susceptibility were detected in North Carolina.
METHODS: We determined the prevalence of I221V among B viruses submitted to the Centers for Disease Control and Prevention for antiviral resistance surveillance, including all B viruses submitted to North Carolina and South Carolina state laboratories, during October 2010-September 2011.We conducted chart reviews and telephone interviews to characterize North Carolina and South Carolina patients with B/I221V vs wild-type B virus infection (B/WT).
RESULTS: We detected I221V in 45 (22%) of 209 B viruses from North Carolina and 8 (10%) of 82 B viruses from South Carolina. We detected I221V in 3 (0.3%) of 881 B viruses tested from 45 other states. B/I221V infection was not associated with differences in underlying conditions or illness severity, compared with B/WT infection. No patients with B/I221V infection received oseltamivir prior to specimen collection. Among patients who completed oseltamivir, those with B/I221V infection reported a longer duration until illness resolution (5 vs 3 days; P = .02).
CONCLUSIONS: B/I221V cocirculated with B/WT in North Carolina and South Carolina during 2010-2011. I221V did not alter illness severity but may have reduced oseltamivir effectiveness. Thus, global surveillance for I221V is important.