Accepted for/Published in: JMIR Public Health and Surveillance
Date Submitted: Dec 26, 2023
Date Accepted: Jun 1, 2024
Increased risk of influenza infection during cold spells in China: National time series study
ABSTRACT
Background:
Studies have reported the adverse effects of cold events on influenza. However, role of critical factors as characteristics of cold spells and regional variation remain unresolved.
Objective:
We aimed to systematically evaluate the association between cold spells and influenza incidence in mainland China.
Methods:
This time series analysis using surveillance data of daily influenza from 325 sites in China for the years 2014–2019. A total of 15 definitions of cold spells were adopted based on combinations of temperature thresholds and days of duration. A distributed lag linear model was used to estimate the short-term effects of cold spells on influenza incidence during the cool seasons (November to March), and we further explored the potential impact of cold spell characteristics (intensity, duration and timing during the season) on the estimated associations. Meta-regressions were used to evaluate the modification effect of city-level socioeconomic indicators.
Results:
The overall effect of cold spells on influenza incidence increased with the temperature threshold used to define cold spells, whereas the added effects were generally small and not statistically significant. The relative risk of influenza-associated with cold spells was 3.35 (95% CI: 2.89-3.88), and the estimated effects were stronger during the middle period of cool seasons. The health effects of cold spells varied geographically and residents in Jiangnan region were vulnerable groups. The overall effects of cold spells were positively correlated with urban population density, population size, GDP per capita and urbanization rate, indicating a sterner response to cold spells forcing in metropolises.
Conclusions:
Cold spells create a substantial health burden on seasonal influenza in China. Findings on regional and socioeconomic differences in the health effects of cold spells on seasonal influenza may be useful in formulating region-specific public health policies to address the hazardous effects of cold spells.
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