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Partial Resistance of Influenza B to Neuraminidase Inhibitors

Emergence of resistant strains and their transmissibility are both worrisome.

Resistance of influenza A to neuraminidase inhibitors (oseltamivir and zanamivir) has been reported, but the prevalence of influenza B resistance is unknown, as is the potential transmissibility of resistant strains.

Researchers used viral isolates from a 2004–2005 influenza B outbreak in Japan (where neuraminidase inhibitor use is particularly common) to study resistance in 74 infected children treated with oseltamivir and 348 infected patients (282 children) not treated with oseltamivir. With use of standard clinical and epidemiologic techniques for identifying resistance and transmissibility, partial neuraminidase inhibitor resistance was found in one treated child (1.4%) and seven untreated patients (2.0%). Of the resistant viruses isolated in the seven untreated patients, four appeared to have been transmitted in community settings, and three within family settings. The clinical course of infections was similar, regardless of resistance.

Comment: These data, while showing a low level of resistance compared with that found in influenza A (5%–18%) and somewhat speculative with regard to transmissibility, are worrisome and deserve follow-up. An editorialist notes that the possible transmissibility of resistant strains (previously thought unlikely) is even more disquieting than the development of resistance itself.

— Thomas L. Schwenk, MD

Published in Journal Watch General Medicine April 3, 2007

Citation(s):

Hatakeyama S et al. Emergence of influenza B viruses with reduced sensitivity to neuraminidase inhibitors. JAMA 2007 Apr 4; 297:1435-42.

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Moscona A and McKimm-Breschkin J. News about influenza B drug resistance that cannot be ignored. JAMA 2007 Apr 4; 297:1492-3.

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