Relationship between temperature and relative humidity on initial spread of COVID-19 cases and related deaths in Brazil

Introduction: Climate conditions may influence the transmission of COVID-19. Thus, the aim of this study was to evaluate the impact of temperature and relative humidity on COVID-19 cases and related deaths during the initial phase of the epidemic in Brazil. Methodology: An ecological study based on secondary data was conducted. Daily data on new COVID-19 cases, deaths, and climate indicators were collected from February 20 to April 18, 2020 (n = 59 days) for all state capital cities in Brazil and the Federal District (Brasília). The climate indicators included mean temperature, temperature amplitude, mean relative humidity, relative humidity amplitude, and percentage of days with mean relative humidity ≤ 65 %. Correlation and multiple linear regression analyses were performed for all cities and stratified by quintiles of the COVID-19 incidence rate. Results: The mean daily temperature was positively correlated with the number of days until the first COVID-19 case was reported. A lower mean relative humidity was correlated with a lower number of cases and deaths in Brazil, especially when the relative humidity was ≤ 65 %. Higher temperatures and humidity amplitudes were correlated with lower COVID-19 mortality. Additionally, after controlling for humidity, cumulative cases of COVID-19 were inversely associated with temperature in cities with mean temperatures less than 25.8 °C. Conclusions: Variations in temperature and humidity across the Brazilian territory may have influenced the spread of the novel coronavirus during the initial phase of the epidemic.