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

Abstract

Introduction The disease transmission pattern of COVID19 is highly heterogeneous, which 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 COVID19 transmission and case fatality worldwide. Methods We assessed SARS CoV2 virus transmission and COVID19 related fatalities in 50 countries in all continents of the globe. Data from the COVID19 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 the incidence data. Disease spread, was assessed using the reproduction number of the disease across the sampled countries. R0 package of R statistical software 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 by taking the R0 value as dependent variable, and latitude and population density as an independent variable. Disease severity was analyzed using the case fatality ratio of COVID19. The proportion of deaths to the total numbers of cases was meta analyzed using metaphor package of R statistical software using random effect inverse variance weighting to come up with the case fatality ratio. Results We 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 COVID19 cases. The relative frequency of people above 65 years old was positively correlated with the cumulative numbers of COVID19 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. An increase in the elderly population proportion by 1 percent was associated with an increase in CFR by 0.32. Correlation with proportion of populations over 65 years old is concordant with the previous findings relationship between case fatality ratio and patient age. Conclusion This 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 COVID19.