Association between growth of the SARS-CoV-2 epidemic and increased coughing rate in cold temperatures: surveillance in Hokkaido, Japan

OBJECTIVE: Although the transmissibility of SARS-CoV-2 in winter is thought to increase through viral droplets when coughing, current epidemiological data in this regard are limited. SETTING: Using the national epidemiological surveillance data in the autumn and winter seasons in Hokkaido, Japan, between February 2020 and February 2021, we analysed the relationship between case increase ratio and prevalence rate of coughing in patients with PCR-confirmed SARS-CoV-2 in two age groups (0—40s and 50—100s) with concomitant air temperature and humidity. PARTICIPANTS: The 7893 cases of symptomatic PCR-positive patients consisted of 5361 cases in the young age group and 2532 cases in the older age group. PRIMARY AND SECONDARY OUTCOME MEASURES: Pearson’s correlation analysis and regression models were used to assess the relationships. Sex-adjusted OR of having cough in the young and old age groups in the autumn and winter seasons was calculated using logistic regression analysis. RESULTS: The monthly prevalence rate of coughing in the young age group was negatively correlated with temperature (r=−0.77, p<0.05), and in the old age group it was negatively correlated with humidity (r=−0.71, p<0.05). Quadratic regression models were fitted for the relationship between cold temperatures and rate of coughing rate in the young age group and case increase ratios. The sex-adjusted OR of having a cough in the young age group in winter was 1.18 (95% CI 1.05 to 1.31) as compared with autumn. CONCLUSIONS: The results suggest increased rate of coughing contributes to the epidemic of SARS-CoV-2 in the winter. An effective control with a focus on these trends should be considered.