Background. The COVID-19 epidemic has had an extreme impact on society. This study aimed to discuss this epidemic in the U.S. and explore the association between COVID-19 daily incidence rate and influencing factors including people’s implementation of states’ quarantine policy and environmental factors including temperature, humidity and so on.
Methods. Data of 50 states in U.S. were used as the research subjects. A panel data model was established based on the daily incidence rate and influencing factors from 15 March to 30 September, 2020. The period was analyzed both unsegmented and segmented. The k-means clustering method was used to cluster the states, and panel linear regression method was used for correlation analysis.
Results. The characteristics of the daily incidence rate and factors of the three categories were different after clustering. The daily residents at home, proportion of travel people, humidity and incidence rate were negatively correlated, while the daily temperature and incidence rate were positively correlated after unsegmented multivariate analysis. While after segmented analysis, the air pressure and the temperature showed a trend that was negatively correlated with the daily incidence rate respectively in the first and the fifth segment, other indicators showed the analogous results. At the same time, this study also completed the regression analysis after classification of the three groups. Compared with results without classification, there was a decrease of the number of significant independent variables.
Conclusions. The spread of COVID-19 in 50 states in U.S. was related to quarantine measures, temperature and humidity. The progress of the epidemic would be relatively slow if people chose to stay at home. Besides, the increase in temperature (＜84.2℉) could be conducive to the spread of the epidemic, while the increase in relative humidity (40~70%) might inhibit the spread of the virus to a certain degree.