Latitudes mediate the association between influenza activity and meteorological factors: A nationwide modelling analysis in 45 Japanese prefectures from 2000 to 2018

Ka Chun Chong; Jingbo Liang; Katherine Min Jia; Nobumichi Kobayashi; Maggie Haitian Wang; Lai Wei; Steven Yuk Fai Lau; Ayako Sumi

doi:10.1016/j.scitotenv.2019.134727

Latitudes mediate the association between influenza activity and meteorological factors: A nationwide modelling analysis in 45 Japanese prefectures from 2000 to 2018

Sci Total Environ. 2020 Feb 10:703:134727. doi: 10.1016/j.scitotenv.2019.134727. Epub 2019 Oct 31.

Authors

Ka Chun Chong¹, Jingbo Liang², Katherine Min Jia³, Nobumichi Kobayashi⁴, Maggie Haitian Wang⁵, Lai Wei², Steven Yuk Fai Lau⁶, Ayako Sumi⁷

Affiliations

¹ JC School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong, China; Clinical Trials and Biostatistics Laboratory, Shenzhen Research Institute, The Chinese University of Hong Kong, China. Electronic address: marc@cuhk.edu.hk.
² JC School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong, China.
³ JC School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong, China. Electronic address: 1155078733@link.cuhk.edu.hk.
⁴ Department of Hygiene, Sapporo Medical University School of Medicine, Sapporo, Japan. Electronic address: nkobayas@sapmed.ac.jp.
⁵ JC School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong, China; Clinical Trials and Biostatistics Laboratory, Shenzhen Research Institute, The Chinese University of Hong Kong, China. Electronic address: maggiew@cuhk.edu.hk.
⁶ JC School of Public Health and Primary Care, The Chinese University of Hong Kong, Hong Kong, China. Electronic address: stevenlau@cuhk.edu.hk.
⁷ Department of Hygiene, Sapporo Medical University School of Medicine, Sapporo, Japan. Electronic address: sumi@sapmed.ac.jp.

PMID: 31731153
DOI: 10.1016/j.scitotenv.2019.134727

Abstract

Background: Cold and dry conditions were well-documented as a major determinant of influenza seasonality in temperate countries but the association may not be consistent when the climate in temperate areas is closer to that in sub-tropical areas. We hypothesized latitudes may mediate the association between influenza activity and meteorological factors in 45 Japanese prefectures.

Methods: We used the weekly incidence of influenza-like illness of 45 prefectures from 2000 to 2018 as a proxy for influenza activity in Japan, a temperate country lying off the east coast of Asia. A combination of generalized additive model and distributed lag nonlinear model was adopted to investigate the associations between meteorological factors (average temperature, relative humidity, total rainfall, and actual vapour pressure, a proxy for absolute humidity) and the influenza incidence. Kendall's tau b (τ) and Spearman correlation coefficient (r_s) between latitude and the adjusted relative risk (ARR) of each meteorological factor were also assessed.

Results: A higher vapour pressure was significantly associated with a lower influenza risk but the ARR strongly weakened along with a lower latitude (τ = -0.23, p-value = 0.02; r_s = -0.33, p-value = 0.03). Lower temperature and lower relatively humidity were significantly associated with higher influenza risks in over 65% and around 40% of the prefectures respectively but the strength and significance of the correlations between their ARRs and latitude were weaker than that from vapour pressure.

Conclusion: Even though the range of latitudes in Japan is small (26°N-43°N), the relationships between meteorological factors and influenza activity were mediated by the latitude. Our study echoed absolute humidity played a more important role in relating influenza risk, but we on the other hand showed its effect on influenza activity could be hampered in a low-latitude temperate region, which have a warmer climate. These findings thus offer a high-resolution characterization of the role of meteorological factors on influenza seasonality.

Keywords: Humidity; Influenza; Japan; Latitude; Temperature.

MeSH terms

Humans
Humidity
Incidence
Influenza, Human*
Japan
Meteorological Concepts
Seasons
Temperature