Reduced norovirus epidemic follows increased sales of hand hygiene products in Japan, 2020-2021.

During the recent emergence of COVID-19, an increased practice of hand hygiene coincided with the reduced incidence of the norovirus epidemic in Japan, which is similar to experience with the pandemic flu in 2009. We investigated the relationship between the sales of hand hygiene products, including liquid hand soap and alcohol-based hand sanitizer, and the trend of norovirus epidemic. We used national gastroenteritis surveillance data across Japan in 2020 and 2021 and compared the base statistics of incidence of these two years with the average of the previous 10 years (2010-2019). We calculated the correlations (Spearman's Rho) between monthly sales of hand hygiene products and monthly norovirus cases and fitted them to a regression model. In 2020, there was no epidemic, and the incidence peak was the lowest in recent norovirus epidemics. In 2021, the incidence peak was delayed for five weeks to the usual epidemic seasons. Correlation coefficients between monthly sales of liquid hand soap and skin antiseptics and norovirus incidence showed a significantly negative correlation (Spearman's Rho = -0.88 and p = 0.002 for liquid hand soap; Spearman's Rho = -0.81 and p = 0.007 for skin antiseptics). Exponential regression models were fitted between the sales of each hand hygiene product and norovirus cases, respectively. The results suggest hand hygiene using these products is a potentially useful prevention method against norovirus epidemics. Effective ways of hand hygiene for increasing the prevention of norovirus should therefore be studied.

Viral transmissibility of SARS-CoV-2 accelerates in the winter, similarly to influenza epidemics.

The transmissibility of SARS-CoV-2 is anticipated to increase in the winter because of increased viral survival in cold damp air and thus would exacerbate viral spread in community. Analysis to capture the seasonal trend is needed to be prepared for future epidemics. We compared regression models for the 5-week case prior to each epidemic peak week for both the COVID-19 and influenza epidemics in winter and summer. The weekly case increase ratio was compared, using non-paired t tests between seasons. In order to test the robustness of seasonal transmission patterns, the normalized weekly case numbers of COVID-19 and influenza case rates of all seasons were assessed in a combined quadratic regression analysis. In winter, the weekly case increase ratio accelerated before epidemic peaks, similarly, for both COVID-19 and influenza. The quadratic regression models of weekly cases were observed to be convex curves in the winter and concave curves in the spring/summer for both COVID-19 and influenza. A significant increase of case increase ratio (3.19 [95%CI:0.01-6.37, P = .049]) of the COVID-19 and influenza epidemics was observed in winter as compared to spring/summer before the epidemic peak. The epidemic of COVID-19 was found to mirror that of influenza, suggesting a strong underlying seasonal transmissibility. Influenza epidemics can potentially be a useful reference for the COVID-19 epidemics.

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.