Climate factors influence seasonal influenza activity in Bangkok, Thailand

RESEARCH ARTICLE Climate factors influence seasonal influenza activity in Bangkok, Thailand Nungruthai Suntronwong, Preeyaporn Vichaiwattana, Sirapa Klinfueng, Sumeth Korkong, Thanunrat Thongmee, Sompong Vongpunsawad, Yong PoovorawanID* Center of Excellence in Clinical Virology, Department of Pediatrics, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand * yong.p@chula.ac.th Abstract Yearly increase in influenza activity is associated with cold and dry winter in the temperate regions, while influenza patterns in tropical countries vary significantly by regional climates and geographic locations. To examine the association between influenza activity in Thailand and local climate factors including temperature, relative humidity, and rainfall, we analyzed the influenza surveillance data from January 2010 to December 2018 obtained from a large private hospital in Bangkok. We found that approximately one in five influenza-like illness samples (21.6% or 6,678/30,852) tested positive for influenza virus. Influenza virus typing showed that 34.2% were influenza A(H1N1)pdm09, 46.0% were influenza A(H3N2), and 19.8% were influenza B virus. There were two seasonal waves of increased influenza activ- ity. Peak influenza A(H1N1)pdm09 activity occurred in February and again in August, while influenza A(H3N2) and influenza B viruses were primarily detected in August and Septem- ber. Time series analysis suggests that increased relative humidity was significantly associ- ated with increased influenza activity in Bangkok. Months with peak influenza activity

generally followed the most humid months of the year. We performed the seasonal autore- gressive integrated moving average (SARIMA) multivariate analysis of all influenza activity on the 2011 to 2017 data to predict the influenza activity for 2018. The resulting model closely resembled the actual observed overall influenza detected that year. Consequently, the ability to predict seasonal pattern of influenza in a large tropical city such as Bangkok may enable better public health planning and underscores the importance of annual influ- enza vaccination prior to the rainy season. Introduction Influenza virus infection is a major cause of acute respiratory disease and contributes to signif- icant morbidity and mortality each year [1]. Seasonal pattern of influenza varies throughout the temperate, tropical and sub-tropical regions of the world [2]. In the temperate regions of both northern and southern hemisphere, influenza activity peaks during the cold winter months and is linked to increased person-to-person transmission in indoor close-contact set- tings and low absolute humidity [3–8]. In tropical regions, different patterns of influenza PLOS ONE PLOS ONE | https://doi.org/10.1371/journal.pone.0239729 September 29, 2020 1 / 15 a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 OPEN ACCESS Citation: Suntronwong N, Vichaiwattana P, Klinfueng S, Korkong S, Thongmee T, Vongpunsawad S, et al. (2020) Climate factors influence seasonal influenza activity in Bangkok, Thailand. PLoS ONE 15(9): e0239729. https://doi. org/10.1371/journal.pone.0239729

Editor: Jeffrey Shaman, Columbia University, UNITED STATES Received: November 26, 2019 Accepted: September 12, 2020 Published: September 29, 2020 Copyright: © 2020 Suntronwong et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Data Availability Statement: All relevant data are within the manuscript and its Supporting Information files. Funding: This work was supported by the Research Chair Grant from the National Science and Technology Development Agency (P-15- 50004) (Y.P.), Center of Excellence in Clinical Virology of Chulalongkorn University and King Chulalongkorn Memorial Hospital (Y.P.). Nungruthai Suntronwong was supported by the Royal Golden Jubilee Ph.D. Program (PHD/0084/