Correlation of the rise and fall in COVID-19 cases with the social isolation index and early outpatient treatment with hydroxychloroquine and chloroquine in the state of Santa Catarina, southern Brazil: A retrospective analysis

BACKGROUND: To contribute to the understanding of the coronavirus disease (COVID-19) pandemic, this study evaluated the correlations of the frequencies of COVID-19 cases, hospitalisations due to COVID-19, and deaths due to COVID-19 with social isolation indices and outpatient prescriptions of hydroxychloroquine and chloroquine in the state of Santa Catarina, southern Brazil. METHODS: This was an analytical, observational, retrospective study based on secondary data that were obtained from public Brazilian databases and covered the period from March 1, 2020 to October 31, 2020 (epidemiological weeks 10–44). Data on weekly COVID-19 cases, hospitalisations and deaths due COVID-19, sales of chloroquine and hydroxychloroquine, and social isolation indices were obtained. Associations between the variables were tested using multiple linear regression analysis. RESULTS: In all regions of Santa Catarina, there were almost simultaneous peaks of COVID-19 pandemic in weeks 28–31, followed by a sudden decrease. Social isolation indices were not associated with the outcomes; sales of chloroquine and hydroxychloroquine were significant predictors of all outcomes (p < 0.001). COVID-19 prevalence was significantly different across the state regions when COVID-19 cases started to decline (p < 0.001). DISCUSSION: Collective immunity and social isolation may not have been the only causes for the reduction of the COVID-19 pandemic observed in Santa Catarina. The results of this study were compatible with the hypothesis that early treatment of COVID-19 cases with chloroquine or hydroxychloroquine may contribute to reducing the transmissibility of COVID-19 in the population. This hypothesis needs to be further tested in future studies.