Open AccessNonannual seasonality of influenza‐like illness in a tropical urban setting
Author(s) -
Lam Ha Minh,
Wesolowski Amy,
Hung Nguyen Thanh,
Nguyen Tran Dang,
Nhat Nguyen Thi Duy,
Todd Stacy,
Vinh Dao Nguyen,
Vy Nguyen Ha Thao,
Thao Tran Thi Nhu,
Thanh Nguyen Thi Le,
Tin Phan Tri,
Minh Ngo Ngoc Quang,
Bryant Juliet E.,
Buckee Caroline O.,
Ngoc Tran Van,
Chau Nguyen Van Vinh,
Thwaites Guy E.,
Farrar Jeremy,
Tam Dong Thi Hoai,
Vinh Ha,
Boni Maciej F.
Publication year - 2018
Publication title -
influenza and other respiratory viruses
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.743
H-Index - 57
eISSN - 1750-2659
pISSN - 1750-2640
DOI - 10.1111/irv.12595
Subject(s) - influenza like illness , medicine , tropics , seasonal influenza , epidemiology , subtropics , outpatient clinic , demography , disease , covid-19 , virus , immunology , biology , infectious disease (medical specialty) , ecology , sociology
Background In temperate and subtropical climates, respiratory diseases exhibit seasonal peaks in winter. In the tropics, with no winter, peak timings are irregular. Methods To obtain a detailed picture of influenza‐like illness (ILI) patterns in the tropics, we established an mHealth study in community clinics in Ho Chi Minh City (HCMC). During 2009‐2015, clinics reported daily case numbers via SMS, with a subset performing molecular diagnostics for influenza virus. This real‐time epidemiology network absorbs 6000 ILI reports annually, one or two orders of magnitude more than typical surveillance systems. A real‐time online ILI indicator was developed to inform clinicians of the daily ILI activity in HCMC. Results From August 2009 to December 2015, 63 clinics were enrolled and 36 920 SMS reports were received, covering approximately 1.7M outpatient visits. Approximately 10.6% of outpatients met the ILI case definition. ILI activity in HCMC exhibited strong nonannual dynamics with a dominant periodicity of 206 days. This was confirmed by time series decomposition, stepwise regression, and a forecasting exercise showing that median forecasting errors are 30%‐40% lower when using a 206‐day cycle. In ILI patients from whom nasopharyngeal swabs were taken, 31.2% were positive for influenza. There was no correlation between the ILI time series and the time series of influenza, influenza A, or influenza B (all P > 0.15). Conclusion This suggests, for the first time, that a nonannual cycle may be an essential driver of respiratory disease dynamics in the tropics. An immunological interference hypothesis is discussed as a potential underlying mechanism.