Journal des maladies infectieuses et de la thérapie

Abstrait

Characterization of Influenza Viruses Responsible for Acute Respiratory Illness in Cambodia from 2015 to 2016

Bonath Ka, Martine Valette, Monidarin Chou and Bruno Lina

Background: Acute Respiratory Infection (ARI) is a leading cause of morbidity and mortality worldwide. During a study describing the circulation and the prevalence of respiratory viruses and bacteria in Cambodia, an ancillary analysis focussed on influenza viruses.

Method: Between July 2015 and December 2016, 18 to 50-year-old patients presenting with ARI (cough+sore throat+fever ≥ 37.5°C) and attending four referral hospitals were included. In each site, out-patients, in-patients and non-ARI controls (outpatients with non-infectious diseases) were recruited. Clinical information and nasal washes were collected. Influenza and other respiratory pathogens were screened by multiplex real-time PCR. Each influenza virus detected was subsequently typed, subtyped, cultured, tested for Neuraminidase Inhibitors susceptibility and sequenced by direct whole genome sequencing.

Results: Amongst the 1006 included patients, 48 were positive for influenza (5.4%), including 36 Influenza A (19 A(H1N1)pdm09 and 17 A(H3N2)), 11 Influenza B (9 Yamagata and 2 Victoria) and one A(H1N1)pdm09+B Victoria co-infection. Overall, 11 in-patients (6 H1N1pdm09, 2 H3N2, 2 B and 1 H1N1pdm09+B co-infection), 36 out-patients (12 A(H1N1)pdm09, 15 A(H3N2) and 9 B) and 1 control (1 H1N1pdm09) were positive. These viruses circulated year-round with 2 peaks during the rainy season (August 2015 and June 2016), and a switch from A(H3N2) to BYamagata
and to A(H1N1)pdm09 with almost no overlap was observed. All viruses were similar to the vaccine strains, and susceptible to NAI.

Conclusion: We report a low prevalence of influenza in this adult population (5.4%). Most cases were due to
influenza A (77.1%) with a balanced distribution between A(H1N1)pdm09 and A(H3N2) (20 vs. 17), and a higher
proportion of A(H1N1)pdm09 in in-patients. No molecular difference was observed between viruses of in- and outpatients,
and no resistance was detected. The year-round circulation and virus switch is similar to this reported in
other sub-tropical areas.