Mutated H1N1 Virus Resistant to Antiviral Drug Oseltamivir

Resistant H1N1 prompts new CDC advisory on prophylactic use of antviral drug
By Jeff Muise
HealthDay Reporter

FRIDAY, Sept. 11 (HealthDay News) -- The discovery of H1N1 mutations resistant to the neuraminidase inhibitor oseltamivir in two adolescent girls sharing a cabin at a North Carolina camp prompted a new recommendation from the U.S. Centers for Disease Control and Prevention on the proper prophylactic use of antiviral drugs, according to a case report in the Sept. 11 issue of the CDC's Morbidity and Mortality Weekly Report.

Michelle Garrison, of the Buncombe County Health Center in North Carolina, and colleagues reported that the two girls were among 418 campers and 189 staff members who underwent prophylactic treatment with either oseltamivir or zanamivir, after an outbreak of an influenza-like illness at the camp in June. The first girl was given oseltamivir at a prophylactic dose which was not increased to a therapeutic dose after symptoms began. Her cabin mate, who also underwent the prophylactic treatment, developed symptoms four days after the first girl's symptoms appeared.

The report further notes that, in late July, the North Carolina State Laboratory confirmed H1N1 virus infection in respiratory specimens from both girls, and in mid-August the CDC detected the H275Y mutation in neuraminidase, which is known to be associated with oseltamivir resistance, in both specimens. A I223V mutation in neuraminidase also was detected. On Sept. 8, the CDC recommended antivirals not be used in healthy persons after possible exposure and be reserved for persons at high risk for influenza-related complications.

"Health care providers should be aware that antiviral resistance can develop during chemoprophylaxis or treatment with subtherapeutic dosages and should follow published recommendations for antiviral medications," the authors conclude.

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