Association between COVID-19 infection rates by region and implementation of non-pharmaceutical interventions: A cross-sectional study in Japan

Background During a pandemic, non-pharmaceutical interventions (NPIs) play an important role in protecting oneself from infection and preventing the spread of infection to others. There are large regional differences in COVID-19 infection rates in Japan. We hypothesized that the local infection incidence may affect adherence to individual NPIs. Methods This cross-sectional study was conducted online among full-time workers in Japan in December 2020. Data from a total of 27,036 participants were analyzed. The questionnaire asked the respondents to identify their habits regarding seven well-known NPIs. Results Compared to the region with the lowest infection rate, the odds ratios for the region with the highest infection rate were 1.24 (p<0.001) for wearing a mask in public, 1.08 (p=0.157) for washing hands after using the bathroom, 1.17 (p=0.031) for disinfecting hands with alcohol sanitizers when entering indoors, 1.54 (p<0.001) for gargling when returning home, 1.45 (p<0.001) for ventilating the room, 1.33 (p<0.001) for disinfecting or washing hands after touching frequently touched surfaces, and 1.32 (p<0.001) for carrying alcohol sanitizers when outdoors. Five of the seven NPIs showed statistically significant trends across regional infection levels, the two exceptions being wearing a mask in public and washing hands after using the bathroom. Multivariate adjustment did not change these trends. Conclusions This study found that NPIs were more prevalent in regions with higher incidence rates of COVID-19 in Japanese workers. The findings suggest that the implementation of NPIs was influenced not only by personal attributes but also by contextual effects of the local infection level.