Seasonality of absolute humidity explains seasonality of influenza-like illness in Vietnam

Pham Quang Thai, Marc Choisy, Tran Nhu Duong, Vu Dinh Thiem, Nguyen Thu Yen, Nguyen Tran Hien, Daniel J. Weiss, Maciej F. Boni, Peter Horby

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

Background: Experimental and ecological studies have shown the role of climatic factors in driving the epidemiology of influenza. In particular, low absolute humidity (AH) has been shown to increase influenza virus transmissibility and has been identified to explain the onset of epidemics in temperate regions. Here, we aim to study the potential climatic drivers of influenza-like illness (ILI) epidemiology in Vietnam, a tropical country characterized by a high diversity of climates. We specifically focus on quantifying and explaining the seasonality of ILI. Methods: We used 18 years (1993-2010) of monthly ILI notifications aggregated by province (52) and monthly climatic variables (minimum, mean, maximum temperatures, absolute and relative humidities, rainfall and hours of sunshine) from 67 weather stations across Vietnam. Seasonalities were quantified from global wavelet spectra, using the value of the power at the period of 1 year as a measure of the intensity of seasonality. The 7 climatic time series were characterized by 534 summary statistics which were entered into a regression tree to identify factors associated with the seasonality of AH. Results were extrapolated to the global scale using simulated climatic times series from the NCEP/NCAR project. Results: The intensity of ILI seasonality in Vietnam is best explained by the intensity of AH seasonality. We find that ILI seasonality is weak in provinces experiencing weak seasonal fluctuations in AH (annual power <17.6), whereas ILI seasonality is strongest in provinces with pronounced AH seasonality (power >17.6). In Vietnam, AH and ILI are positively correlated. Conclusions: Our results identify a role for AH in driving the epidemiology of ILI in a tropical setting. However, in contrast to temperate regions, high rather than low AH is associated with increased ILI activity. Fluctuation in AH may be the climate factor that underlies and unifies the seasonality of ILI in both temperate and tropical regions. Alternatively, the mechanism of action of AH on disease transmission may be different in cold-dry versus hot-humid settings.

Original languageEnglish (US)
Pages (from-to)65-73
Number of pages9
JournalEpidemics
Volume13
DOIs
StatePublished - Jan 1 2015

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Vietnam
Humidity
Human Influenza
Epidemiology
Climate
Sunlight
Weather
Orthomyxoviridae
Temperature

All Science Journal Classification (ASJC) codes

  • Epidemiology
  • Parasitology
  • Microbiology
  • Public Health, Environmental and Occupational Health
  • Infectious Diseases
  • Virology

Cite this

Thai, P. Q., Choisy, M., Duong, T. N., Thiem, V. D., Yen, N. T., Hien, N. T., ... Horby, P. (2015). Seasonality of absolute humidity explains seasonality of influenza-like illness in Vietnam. Epidemics, 13, 65-73. https://doi.org/10.1016/j.epidem.2015.06.002
Thai, Pham Quang ; Choisy, Marc ; Duong, Tran Nhu ; Thiem, Vu Dinh ; Yen, Nguyen Thu ; Hien, Nguyen Tran ; Weiss, Daniel J. ; Boni, Maciej F. ; Horby, Peter. / Seasonality of absolute humidity explains seasonality of influenza-like illness in Vietnam. In: Epidemics. 2015 ; Vol. 13. pp. 65-73.
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Thai, PQ, Choisy, M, Duong, TN, Thiem, VD, Yen, NT, Hien, NT, Weiss, DJ, Boni, MF & Horby, P 2015, 'Seasonality of absolute humidity explains seasonality of influenza-like illness in Vietnam', Epidemics, vol. 13, pp. 65-73. https://doi.org/10.1016/j.epidem.2015.06.002

Seasonality of absolute humidity explains seasonality of influenza-like illness in Vietnam. / Thai, Pham Quang; Choisy, Marc; Duong, Tran Nhu; Thiem, Vu Dinh; Yen, Nguyen Thu; Hien, Nguyen Tran; Weiss, Daniel J.; Boni, Maciej F.; Horby, Peter.

In: Epidemics, Vol. 13, 01.01.2015, p. 65-73.

Research output: Contribution to journalArticle

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T1 - Seasonality of absolute humidity explains seasonality of influenza-like illness in Vietnam

AU - Thai, Pham Quang

AU - Choisy, Marc

AU - Duong, Tran Nhu

AU - Thiem, Vu Dinh

AU - Yen, Nguyen Thu

AU - Hien, Nguyen Tran

AU - Weiss, Daniel J.

AU - Boni, Maciej F.

AU - Horby, Peter

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AB - Background: Experimental and ecological studies have shown the role of climatic factors in driving the epidemiology of influenza. In particular, low absolute humidity (AH) has been shown to increase influenza virus transmissibility and has been identified to explain the onset of epidemics in temperate regions. Here, we aim to study the potential climatic drivers of influenza-like illness (ILI) epidemiology in Vietnam, a tropical country characterized by a high diversity of climates. We specifically focus on quantifying and explaining the seasonality of ILI. Methods: We used 18 years (1993-2010) of monthly ILI notifications aggregated by province (52) and monthly climatic variables (minimum, mean, maximum temperatures, absolute and relative humidities, rainfall and hours of sunshine) from 67 weather stations across Vietnam. Seasonalities were quantified from global wavelet spectra, using the value of the power at the period of 1 year as a measure of the intensity of seasonality. The 7 climatic time series were characterized by 534 summary statistics which were entered into a regression tree to identify factors associated with the seasonality of AH. Results were extrapolated to the global scale using simulated climatic times series from the NCEP/NCAR project. Results: The intensity of ILI seasonality in Vietnam is best explained by the intensity of AH seasonality. We find that ILI seasonality is weak in provinces experiencing weak seasonal fluctuations in AH (annual power <17.6), whereas ILI seasonality is strongest in provinces with pronounced AH seasonality (power >17.6). In Vietnam, AH and ILI are positively correlated. Conclusions: Our results identify a role for AH in driving the epidemiology of ILI in a tropical setting. However, in contrast to temperate regions, high rather than low AH is associated with increased ILI activity. Fluctuation in AH may be the climate factor that underlies and unifies the seasonality of ILI in both temperate and tropical regions. Alternatively, the mechanism of action of AH on disease transmission may be different in cold-dry versus hot-humid settings.

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