Epidemiological and Virological Characteristics of Influenza Viruses Circulating in Cambodia from 2009 to 2011

Abstract

BackgroundThe Cambodian National Influenza Center (NIC) monitored and characterized circulating influenza strains from 2009 to 2011.Methodology/Principal FindingsSentinel 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/SignificanceIn 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.

Genetic Characterization of Circulating 2015 A(H1N1)pdm09 Influenza Viruses from Eastern India

“…Analysis of the receptor-binding domain (RBD 63-286 ) revealed at least eleven mutations in HA1 polypeptide. The characteristic genogroup 6 amino acid change at S203T was observed in all viruses examined in the present study [22,23]. In addition, P83S and I321V mutations were also observed in all isolates.…”

Establishing seasonal and alert influenza thresholds in Cambodia using the WHO method: implications for effective utilization of influenza surveillance in the tropics and subtropics

“…Viral RNA was extracted using commercial extraction kits and amplified with reverse transcription polymerase chain reaction (RT–PCR) using standard protocols. ( 12 , 13 )…”

“…Influenza season was defined to start when the parameter increased above the seasonal threshold and to end when the parameter declined below the threshold. The number of times per year the seasonal threshold was crossed was used to assess the validity of the seasonal threshold; assuming one influenza season per year in Cambodia based on historic data, ( 10 , 12 , 13 ) additional detected seasons were considered false alarms. We also compared results from two conventional rules to declare season onset: the first-week-declaration rule, where onset is declared on the first week the threshold is crossed and the two-consecutive-week-declaration rule, where onset is declared when the threshold is crossed for two consecutive weeks.…”

“…( 12 , 13 ) Using the proportion of influenza-like illness (ILI) patient samples positive for influenza, the influenza season appeared to be between June and December, coinciding with the rainy season. However, such findings have not yet been fully used for routine public health practice.…”

Using a hospital admission survey to estimate the burden of influenza‐associated severe acute respiratory infection in one province of Cambodia—methods used and lessons learned

“…Cambodia has conducted influenza surveillance since 2009, including both outpatient influenza‐like illness surveillance and hospitalized SARI surveillance, and enrolls all patients meeting the Cambodia SARI case definition at eight sentinel surveillance sites. Surveillance has demonstrated that influenza viruses commonly circulate during the rainy season (June‐November) in Cambodia each year 13, 14. Between 2009 and 2014, influenza circulation peaked between August and November; influenza positivity among SARI cases fluctuated from 12% in 2009 to 3% in 2014 15…”