title: Epidemiological and virological characteristics of influenza viruses circulating in Cambodia from 2009 to 2011.
abstract: BACKGROUND
  The Cambodian National Influenza Center (NIC) monitored and characterized circulating influenza strains from 2009 to 2011.
  
  
  RESULTS
  Sentinel and study sites collected nasopharyngeal specimens for diagnostic detection, virus isolation, antigenic characterization, sequencing and antiviral susceptibility analysis from patients who fulfilled case definitions for influenza-like illness, acute lower respiratory infections and event-based surveillance. Each year in Cambodia, influenza viruses were detected mainly from June to November, during the rainy season. Antigenic analysis show that A/H1N1pdm09 isolates belonged to the A/California/7/2009-like group. Circulating A/H3N2 strains were A/Brisbane/10/2007-like in 2009 before drifting to A/Perth/16/2009-like in 2010 and 2011. The Cambodian influenza B isolates from 2009 to 2011 all belonged to the B/Victoria lineage represented by the vaccine strains B/Brisbane/60/2008 and B/Malaysia/2506/2004. Sequences of the M2 gene obtained from representative 2009-2011 A/H3N2 and A/H1N1pdm09 strains all contained the S31N mutation associated with adamantanes resistance except for one A/H1N1pdm09 strain isolated in 2011 that lacked this mutation. No reduction in the susceptibility to neuraminidase inhibitors was observed among the influenza viruses circulating from 2009 to 2011. Phylogenetic analysis revealed that A/H3N2 strains clustered each year to a distinct group while most A/H1N1pdm09 isolates belonged to the S203T clade.
  
  
  CONCLUSIONS
  In Cambodia, from 2009 to 2011, influenza activity occurred throughout the year with peak seasonality during the rainy season from June to November. Seasonal influenza epidemics were due to multiple genetically distinct viruses, even though all of the isolates were antigenically similar to the reference vaccine strains. The drug susceptibility profile of Cambodian influenza strains revealed that neuraminidase inhibitors would be the drug of choice for influenza treatment and chemoprophylaxis in Cambodia, as adamantanes are no longer expected to be effective.
authors.affiliation: Institut Pasteur du Cambodge, Réseau International des Instituts Pasteur, Phnom Penh, Cambodia.
authors.forename: Srey Viseth
authors.initials: SV
authors.lastname: Horm
authors.affiliation: Institut Pasteur du Cambodge, Réseau International des Instituts Pasteur, Phnom Penh, Cambodia; World Health Organization, Phnom Penh, Cambodia.
authors.forename: Sek
authors.initials: S
authors.lastname: Mardy
authors.affiliation: Institut Pasteur du Cambodge, Réseau International des Instituts Pasteur, Phnom Penh, Cambodia.
authors.forename: Sareth
authors.initials: S
authors.lastname: Rith
authors.affiliation: Communicable Disease Control Department, Ministry of Health, Phnom Penh, Cambodia.
authors.forename: Sovann
authors.initials: S
authors.lastname: Ly
authors.affiliation: Communicable Disease Control Department, Ministry of Health, Phnom Penh, Cambodia.
authors.forename: Seng
authors.initials: S
authors.lastname: Heng
authors.affiliation: Institut Pasteur du Cambodge, Réseau International des Instituts Pasteur, Phnom Penh, Cambodia.
authors.forename: Sirenda
authors.initials: S
authors.lastname: Vong
authors.affiliation: Influenza Division, National Center for Immunization and Respiratory Disease, Center for Disease Control and Prevention, Atlanta, Georgia, United States of America.
authors.forename: Paul
authors.initials: P
authors.lastname: Kitsutani
authors.affiliation: World Health Organization, Phnom Penh, Cambodia.
authors.forename: Vannra
authors.initials: V
authors.lastname: Ieng
authors.affiliation: Institut Pasteur du Cambodge, Réseau International des Instituts Pasteur, Phnom Penh, Cambodia.
authors.forename: Arnaud
authors.initials: A
authors.lastname: Tarantola
authors.affiliation: Institut Pasteur du Cambodge, Réseau International des Instituts Pasteur, Phnom Penh, Cambodia.
authors.forename: Sowath
authors.initials: S
authors.lastname: Ly
authors.affiliation: Centers for Disease Control and Prevention, Cambodia Office, Phnom Penh, Cambodia.
authors.forename: Borann
authors.initials: B
authors.lastname: Sar
authors.affiliation: Centers for Disease Control and Prevention, Cambodia Office, Phnom Penh, Cambodia.
authors.forename: Nora
authors.initials: N
authors.lastname: Chea
authors.affiliation: National Institute of Public Health, Phnom Penh, Cambodia.
authors.forename: Buth
authors.initials: B
authors.lastname: Sokhal
authors.affiliation: WHO Collaborating Centre for Reference and Research on Influenza, Melbourne, Australia.
authors.forename: Ian
authors.initials: I
authors.lastname: Barr
authors.affiliation: WHO Collaborating Centre for Reference and Research on Influenza, Melbourne, Australia.
authors.forename: Anne
authors.initials: A
authors.lastname: Kelso
authors.affiliation: Institut Pasteur du Cambodge, Réseau International des Instituts Pasteur, Phnom Penh, Cambodia.
authors.forename: Paul F
authors.initials: PF
authors.lastname: Horwood
authors.affiliation: Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.
authors.forename: Ans
authors.initials: A
authors.lastname: Timmermans
authors.affiliation: WHO Collaborating Centre for Reference and Research on Influenza, Melbourne, Australia.
authors.forename: Aeron
authors.initials: A
authors.lastname: Hurt
authors.affiliation: Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.
authors.forename: Chanthap
authors.initials: C
authors.lastname: Lon
authors.affiliation: Armed Forces Research Institute of Medical Sciences, Bangkok, Thailand.
authors.forename: David
authors.initials: D
authors.lastname: Saunders
authors.affiliation: National Institute of Public Health, Phnom Penh, Cambodia.
authors.forename: Sam An
authors.initials: SA
authors.lastname: Ung
authors.affiliation: World Health Organization, Phnom Penh, Cambodia.
authors.forename: Nima
authors.initials: N
authors.lastname: Asgari
authors.affiliation: World Health Organization, Phnom Penh, Cambodia.
authors.forename: Maria Concepcion
authors.initials: MC
authors.lastname: Roces
authors.affiliation: Communicable Disease Control Department, Ministry of Health, Phnom Penh, Cambodia.
authors.forename: Sok
authors.initials: S
authors.lastname: Touch
authors.affiliation: WHO Collaborating Centre for Reference and Research on Influenza, Melbourne, Australia.
authors.forename: Naomi
authors.initials: N
authors.lastname: Komadina
authors.affiliation: Institut Pasteur du Cambodge, Réseau International des Instituts Pasteur, Phnom Penh, Cambodia.
authors.forename: Philippe
authors.initials: P
authors.lastname: Buchy
mesh_terms: D000818:Animals; D000956:Antigens, Viral / Q000276:immunology; D002160:Cambodia / Q000453:epidemiology; D004285:Dogs; D024882:Drug Resistance, Viral; D019267:Hemagglutinin Glycoproteins, Influenza Virus / Q000235:genetics; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000235:genetics / Q000302:isolation & purification; D053122:Influenza A Virus, H3N2 Subtype / Q000235:genetics / Q000302:isolation & purification; D009981:Influenza B virus / Q000235:genetics / Q000302:isolation & purification; D007252:Influenza Vaccines / Q000276:immunology; D007251:Influenza, Human / Q000453:epidemiology* / Q000276:immunology / Q000821:virology*; D061985:Madin Darby Canine Kidney Cells; D009975:Orthomyxoviridae / Q000276:immunology / Q000302:isolation & purification / Q000502:physiology*; D010802:Phylogeny; D012621:Seasons
chemical_list: D000956:Antigens, Viral; D019267:Hemagglutinin Glycoproteins, Influenza Virus; D007252:Influenza Vaccines