title: Surveillance for neuraminidase inhibitor resistance among human influenza A and B viruses circulating worldwide from 2004 to 2008.
abstract: The surveillance of seasonal influenza virus susceptibility to neuraminidase (NA) inhibitors was conducted using an NA inhibition assay. The 50% inhibitory concentration values (IC(50)s) of 4,570 viruses collected globally from October 2004 to March 2008 were determined. Based on mean IC(50)s, A(H3N2) viruses (0.44 nM) were more sensitive to oseltamivir than A(H1N1) viruses (0.91 nM). The opposite trend was observed with zanamivir: 1.06 nM for A(H1N1) and 2.54 nM for A(H3N2). Influenza B viruses exhibited the least susceptibility to oseltamivir (3.42 nM) and to zanamivir (3.87 nM). To identify potentially resistant viruses (outliers), a threshold of a mean IC(50) value + 3 standard deviations was defined for type/subtype and drug. Sequence analysis of outliers was performed to identify NA changes that might be associated with reduced susceptibility. Molecular markers of oseltamivir resistance were found in six A(H1N1) viruses (H274Y) and one A(H3N2) virus (E119V) collected between 2004 and 2007. Some outliers contained previously reported mutations (e.g., I222T in the B viruses), while other mutations [e.g., R371K and H274Y in B viruses and H274N in A(H3N2) viruses) were novel. The R371K B virus outlier exhibited high levels of resistance to both inhibitors (>100 nM). A substantial variance at residue D151 was observed among A(H3N2) zanamivir-resistant outliers. The clinical relevance of newly identified NA mutations is unknown. A rise in the incidence of oseltamivir resistance in A(H1N1) viruses carrying the H274Y mutation was detected in the United States and in other countries in the ongoing 2007 to 2008 season. As of March 2008, the frequency of resistance among A(H1N1) viruses in the United States was 8.6% (50/579 isolates). The recent increase in oseltamivir resistance among A(H1N1) viruses isolated from untreated patients raises public health concerns and necessitates close monitoring of resistance to NA inhibitors.
authors.affiliation: Influenza Division, National Center for Immunization and Respiratory Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia 30333, USA.
authors.forename: Tiffany G
authors.initials: TG
authors.lastname: Sheu
authors.forename: Varough M
authors.initials: VM
authors.lastname: Deyde
authors.forename: Margaret
authors.initials: M
authors.lastname: Okomo-Adhiambo
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Garten
authors.forename: Xiyan
authors.initials: X
authors.lastname: Xu
authors.forename: Rick A
authors.initials: RA
authors.lastname: Bright
authors.forename: Eboneé N
authors.initials: EN
authors.lastname: Butler
authors.forename: Teresa R
authors.initials: TR
authors.lastname: Wallis
authors.forename: Alexander I
authors.initials: AI
authors.lastname: Klimov
authors.forename: Larisa V
authors.initials: LV
authors.lastname: Gubareva
mesh_terms: D000818:Animals; D000998:Antiviral Agents / Q000494:pharmacology / Q000627:therapeutic use; D002460:Cell Line; D024882:Drug Resistance, Viral; D014943:Global Health; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D053122:Influenza A Virus, H3N2 Subtype / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics*; D009981:Influenza B virus / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D007251:Influenza, Human / Q000453:epidemiology* / Q000821:virology; D009439:Neuraminidase / Q000037:antagonists & inhibitors* / Q000235:genetics; D053139:Oseltamivir / Q000494:pharmacology / Q000627:therapeutic use; D011159:Population Surveillance; D012621:Seasons
chemical_list: D000998:Antiviral Agents; D053139:Oseltamivir; D009439:Neuraminidase