Drug-resistant influenza becoming a trickier target
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Viruses resistant to antiviral medications are a growing problem, according to a study in The Netherlands.
“After monitoring antiviral resistance patterns during three subsequent influenza seasons in the Netherlands, we described the unpredictable nature of the emergence of antiviral resistance patterns.” Dr. Marcel Jonges told Reuters Health, referring to his team’s report in the September issue of Antiviral Research.
“This means,” he continued, “that effective treatment or prophylaxis of influenza is becoming more and more complicated, since hospitals and nursing homes cannot base appropriate antiviral therapy on national influenza surveillance drug susceptibility data.”
The investigators, all from the National Institute for Public Health and the Environment in Bilthoven, analyzed the antiviral susceptibility profiles of 273 isolates gathered between 2005 and 2008.
The proportion of adamantane-resistant A(H3N2) viruses increased from 74% in 2005-2007, to 100% in 2007-2008. However, all isolated A(H1N1) viruses were sensitive. The presence or absence of S31N mutations in M2 protein was the major determinant of adamantane resistance.
Prior to 2007-2008, 98% of types A and B influenza viruses were sensitive to both oseltamivir and zanamivir. In 2007-2008, however, 24% of the A(H1N1) viruses were oseltamivir-resistant. They remained sensitive to zanamivir and the adamantanes, however.
The oseltamivir-resistant A(H1N1) or adamantane-resistant A(H3N2) viruses and the sensitive variants produced similar clinical symptoms, the report indicates.
Given these findings, Dr. Jonges says, “Fast and reliable point-of-care antiviral resistance tests are needed to start treatment with the functional antiviral drug, and monitor the emergence of resistance during treatment.”
Antiviral Res 2009;83:290-297.
By David Douglas
NEW YORK (Reuters Health)
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