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
National Institute of Hygiene and Epidemiology, Hanoi, Viet Nam; Wellcome Trust Major Overseas Programme, Oxford University Clinical Research Unit, Hanoi, Viet Nam.
Wellcome Trust Major Overseas Programme, Oxford University Clinical Research Unit, Hanoi, Viet Nam; MIVEGEC, University of Montpellier, CNRS 5290, IRD 224, Montpellier, France.
Epidemics. 2015 Dec;13:65-73. doi: 10.1016/j.epidem.2015.06.002. Epub 2015 Aug 28.
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.
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.
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.
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.
实验和生态学研究表明气候因素在推动流感流行病学方面发挥着作用。特别是，低绝对湿度（AH）已被证明会增加流感病毒的传播能力，并被认为可以解释温带地区流感流行的发生。在此，我们旨在研究越南这个气候高度多样的热带国家中，影响流感样疾病（ILI）流行病学的潜在气候驱动因素。我们特别关注量化和解释ILI的季节性。
我们使用了18年（1993 - 2010年）按省份（52个）汇总的每月ILI报告数据，以及越南67个气象站的每月气候变量（最低、平均、最高温度、绝对湿度和相对湿度、降雨量和日照小时数）。通过全球小波谱对季节性进行量化，将1年周期的功率值用作季节性强度的度量。这7个气候时间序列由534个汇总统计数据表征，这些数据被输入到回归树中以识别与AH季节性相关的因素。使用来自NCEP/NCAR项目的模拟气候时间序列将结果外推到全球尺度。
越南ILI季节性的强度最好由AH季节性的强度来解释。我们发现，在AH季节性波动较弱（年功率<17.6）的省份，ILI季节性较弱；而在AH季节性明显（功率>17.6）的省份，ILI季节性最强。在越南，AH与ILI呈正相关。
我们的结果表明AH在热带环境中推动ILI流行病学方面发挥了作用。然而，与温带地区不同，高AH而非低AH与ILI活动增加相关。AH的波动可能是温带和热带地区ILI季节性的潜在气候因素且使其具有一致性。或者，AH对疾病传播的作用机制在冷干与湿热环境中可能有所不同。
