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. 2022 Aug;10(8):e1150-e1158.
doi: 10.1016/S2214-109X(22)00212-1. Epub 2022 Jun 13.

Seasonality of influenza and coseasonality with avian influenza in Bangladesh, 2010-19: a retrospective, time-series analysis

Isha Berry  1 , Mahbubur Rahman  2 , Meerjady Sabrina Flora  3 , Tahmina Shirin  2 , A S M Alamgir  2 , Manjur Hossain Khan  2 , Rubaid Anwar  2 , Mona Lisa  2 , Fahmida Chowdhury  4 , Md Ariful Islam  4 , Muzzafar G Osmani  5 , Stacie Dunkle  6 , Eric Brum  6 , Amy L Greer  7 , Shaun K Morris  8 , Punam Mangtani  9 , David N Fisman  10
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Free article

Seasonality of influenza and coseasonality with avian influenza in Bangladesh, 2010-19: a retrospective, time-series analysis

Isha Berry et al. Lancet Glob Health. 2022 Aug.
Free article

Abstract

Background: Seasonal and avian influenza viruses circulate among human and poultry populations in Bangladesh. However, the epidemiology of influenza is not well defined in this setting. We aimed to characterise influenza seasonality, examine regional heterogeneity in transmission, and evaluate coseasonality between circulating influenza viruses in Bangladesh.

Methods: In this retrospective, time-series study, we used data collected between January, 2010, and December, 2019, from 32 hospital-based influenza surveillance sites across Bangladesh. We estimated influenza peak timing and intensity in ten regions using negative binomial harmonic regression models, and applied meta-analytic methods to determine whether seasonality differed across regions. Using live bird market surveillance data in Dhaka, Bangladesh, we estimated avian influenza seasonality and examined coseasonality between human and avian influenza viruses.

Findings: Over the 10-year study period, we included 8790 human influenza cases and identified a distinct influenza season, with an annual peak in June to July each year (peak calendar week 27·6, 95% CI 26·7-28·6). Epidemic timing varied by region (I2=93·9%; p<0·0001), with metropolitan regions peaking earlier and epidemic spread following a spatial diffusion pattern based on geographical proximity. Comparatively, avian influenza displayed weak seasonality, with moderate year-round transmission and a small peak in April (peak calendar week 14·9, 95% CI 13·2-17·0), which was out of phase with influenza peaks in humans.

Interpretation: In Bangladesh, influenza prevention and control activities could be timed with annual seasonality, and regional heterogeneity should be considered in health resource planning. Year-round avian influenza transmission poses a risk for viral spillover, and targeted efforts will be crucial for mitigating potential reassortment and future pandemic threats.

Funding: Canadian Institute of Health Research Vanier Canada Graduate Scholarship.

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Conflict of interest statement

Declaration of interests DNF has received support by a grant from the Canadian Institutes for Health Research (2019 COVID-19 rapid researching funding OV4-170360). DNF has served as a legal expert on issues related to COVID-19 epidemiology for the Elementary Teachers Federation of Ontario and the Registered Nurses Association of Ontario. DNF has served on advisory boards related to influenza and SARS-CoV-2 vaccines for Seqirus, Pfizer, AstraZeneca, and Sanofi-Pasteur vaccines. All other authors declare no competing interests.

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