Trends of SARS-CoV-2 infection worldwide: Role of population density, age structure, and climate on transmission and case fatality

IntroductionThe highly heterogenous disease transmission pattern of COVID-19 suggests that the pandemic maybe driven by complex factors, which may include habitat suitability, region specific human mobility, and transmission related to susceptibility. The purpose of this study was to examine the effects of different spatial and demographic factors on COVID-19 transmission and case fatality worldwide. MethodsWe assessed SARS-CoV-2 virus transmission and COVID-19 related fatalities in 50 countries in all continents of the globe. Data from the COVID-19 data repository of the Johns Hopkins Center for Systems Science and Engineering, the European center for disease control and prevention, and the World Health Organization were used to obtain the daily number of cases and organize incidence data. Disease spread was assessed using the reproduction number of the disease across the sampled countries. R statistical softwares R0 package was used to estimate the reproduction number of the COVID19 using the exponential growth method. After computing the reproductive number of each country in the study, a multiple linear regression model was fitted using R0 value as dependent variable, and latitude and population density as an independent variable. Disease severity was analyzed using the case fatality ratio of COVID-19. The proportion of deaths were meta-analyzed using the R statistical softwares metaphor package, using random effect inverse variance weighting to come up with the case fatality ratio. ResultsWe found no statistically significant association between disease spread and latitude or population density. The regression model analysis that accounted for age, population density and latitude showed that age distribution remains an important driver shaping the current distribution of COVID-19 cases. The relative frequency of people above 65 years old was positively correlated with the cumulative numbers of COVID-19 cases as well as case fatality ratio in each country. The multiple linear regression model fitted between CFR and the three major covariates showed that, the demographic distribution of the sampled countries is strongly associated with the case fatality ratio. Correlation with proportion of populations over 65 years old is concordant with the previous findings relationship between case fatality ratio and patient age. ConclusionThis analysis provides important information that can inform the decisions of local and global health authorities. Particularly, as our study confirms that death and severity of COVID19 are associated with age, in countries with the biggest outbreaks, strategies must be employed to ensure that high-risk groups, such as old people received adequate protection from COVID-19.