title: Oseltamivir resistance among influenza viruses: surveillance in northern Viet Nam, 2009-2012.
abstract: BACKGROUND
  Antiviral resistance has been reported in seasonal influenza A viruses and avian influenza A(H5N1) viruses in Viet Nam, raising concerns about the efficacy of treatment.
  
  
  METHODS
  We analysed specimens from two sources during the period 2009-2012: influenza-positive samples from influenza-like illness patients at sentinel clinics in northern Viet Nam and isolates from patients with confirmed A(H5N1) infections. Pyrosequencing was used to detect mutations: H275Y [for A(H1N1) and A(H5N1)], E119V [for A(H3N2)] and I117V [for A(H5N1)]. A neuraminidase inhibition assay was used to determine the Inhibitory Concentration 50 (IC₅₀) values for all influenza A and B isolates.
  
  
  RESULTS
  There were 341 influenza A positive samples identified; influenza A(H1N1)pdm09 was identified most frequently (n = 215). In 2009, oseltamivir resistance was observed in 100% (19 of 19) of seasonal A(H1N1) isolates and 1.4% (3/215) of A(H1N1)pdm09 isolates. This H275Y mutation was not found in influenza subtypes A(H5N1) or A(H3N2) isolates.
  
  
  CONCLUSIONS
  In Viet Nam, seasonal and A(H5N1) influenza vaccines are not currently available; thus, effective treatment is required. The presence of oseltamivir-resistant viruses is therefore a concern. Active surveillance for oseltamivir resistance among influenza viruses circulating in Viet Nam should be continued.
authors.affiliation: National Influenza Center, National Institute of Hygiene and Epidemiology, Hanoi, Vietnam.
authors.forename: Mai-Phuong
authors.initials: MP
authors.lastname: Hoang Vu
authors.forename: Co Thach
authors.initials: CT
authors.lastname: Nguyen
authors.forename: Le Khanh Hang
authors.initials: le KH
authors.lastname: Nguyen
authors.forename: Thi Kim Phuong
authors.initials: TK
authors.lastname: Nguyen
authors.forename: Quynh Mai
authors.initials: QM
authors.lastname: Le
mesh_terms: D000998:Antiviral Agents / Q000008:administration & dosage* / Q000494:pharmacology; D024882:Drug Resistance, Viral / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000008:administration & dosage* / Q000494:pharmacology; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000187:drug effects; D053122:Influenza A Virus, H3N2 Subtype / Q000187:drug effects; D053124:Influenza A Virus, H5N1 Subtype / Q000187:drug effects; D009981:Influenza B virus / Q000187:drug effects*; D007251:Influenza, Human / Q000188:drug therapy* / Q000453:epidemiology; D009154:Mutation / Q000187:drug effects; D053139:Oseltamivir / Q000008:administration & dosage* / Q000494:pharmacology; D011159:Population Surveillance; D014744:Vietnam / Q000453:epidemiology
chemical_list: D000998:Antiviral Agents; D004791:Enzyme Inhibitors; D053139:Oseltamivir