Detection of human influenza A (H1N1) and B strains with reduced sensitivity to neuraminidase inhibitors

Journal of Clinical Virology

Volume 41, Issue 1, Pages 25-28 (January 2008)


Emilie Froberta, Maude Bouscambert-Duchampa, Murielle Sabatiera, Isidore Grogc, Martine Valetteb, Bruno Linaab, Florence Morfina, Olivier Ferrarisa



Neuraminidase inhibitors (NAIs) have been used since 2005 in France.


Influenza viruses isolated in hospital and community cases in winter 2005–2006 were evaluated for their sensitivity to NAIs.

Study design

Isolates were tested in duplicate with a fluorescence-based neuraminidase assay. The IC50 for oseltamivir or zanamivir was calculated for each strain. Mean IC50 (±S.D.) are expressed in nM. Viruses with IC50 superior or very superior to the upper limit (mean IC50+2.5 S.D.) were considered as outliers or resistant viruses, respectively. HA and NA genes for outliers, resistant strains and for a few sensitive strains were sequenced.


Out of 225 B isolates, one was found resistant to both oseltamivir and zanamivir with a D197Y mutation in NA and eight isolates were outliers for oseltamivir and/or zanamivir. Out of 151 A (H1N1) isolates, one was found resistant to oseltamivir but sensitive to zanamivir with a H275Y mutation in NA, two isolates were resistant to zanamivir and three isolates were outliers for oseltamivir and/or zanamivir. New mutations were detected in outliers compared to sensitive viruses.


Resistant influenza strains to NAIs are circulating at a stable and low level of 1% since the introduction of NAIs in clinical practice.


Supported  by

Yudhasmara Foundation

JL Taman Bendungan Asahan 5 Jakarta Indonesia 102010

phone : 62(021) 70081995 – 5703646




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