Lessons and concerns about the SARS-CoV-2/DENV co-infection.

Brazil has experienced frequent epidemic cycles of dengue virus infection over the past five decades. In addition, the country ranked among the most affected globally in terms of the number of cases and deaths caused by SARS-CoV-2 infection during 2020 and 2021, when the world faced the COVID-19 pandemic. Currently, a new dengue outbreak is underway, accompanied by a rising number of SARS-CoV-2 infections, which may lead to a severe collapse of the public health system. The primary aim of this retrospective cohort study was to investigate the occurrence of SARS-CoV-2 seropositivity in a panel of serum samples collected from patients presenting with clinical signs and symptoms of dengue virus infection in the Triângulo Mineiro Norte region, Minas Gerais State, Brazil. The period from January 2019 to April 2021 was selected to capture the dynamics across both the pre-pandemic and pandemic phases, prior to the implementation of the COVID-19 vaccination campaign. A total of 2,969 serum samples from patients residing in the region were analyzed using a Dengue IgM Capture ELISA and a COVID-19 IgG/IgM rapid test device. Although the primary diagnostic hypothesis for all samples was dengue infection, as the pandemic progressed, the number of SARS-CoV-2-positive samples surpassed that of dengue-positive samples. In conclusion, although both viral infections occurred independently, without an apparent causal relationship, our findings suggest that the true number of SARS-CoV-2 infections was significantly underestimated during the study period, thereby increasing the risk of severe COVID-19 outcomes, particularly in a population already experiencing co-infection with dengue virus.