High Mortality Associated with Chikungunya Epidemic in Southeast Brazil, 2023

Abstract The chikungunya virus (CHIKV) was first detected in Brazil in 2014 with two lineages, North Asia and ECSA (East/Central/South Africa). The ECSA lineage dominated, causing significant outbreaks, especially in densely populated areas. The co-circulation of dengue and chikungunya has complicated diagnosis and treatment. The 2023 chikungunya epidemic in Minas Gerais, Southeast Brazil, prompted an assessment of associated mortality using WHO methodologies. The study used epidemiological data from the laboratory surveillance, disease notification and mortality systems of the Brazilian Ministry of Health. The North and Northeast Health Macroregions of Minas Gerais, with 2.5 million inhabitants, were analyzed. A Poisson regression model, excluding critical periods of COVID-19 and the chikungunya epidemic, estimated expected mortality. Excess deaths were calculated by comparing observed deaths with model estimates during the epidemic period. During the epidemic, there were 890 excess deaths attributed to chikungunya, translating into a mortality rate of 35.1/100,000 inhabitants. The excess mortality rate was significantly 60 times higher than the deaths reported by surveillance, with only 15 deaths confirmed. The correlation between excess deaths and laboratory-confirmed chikungunya cases was strong, while the correlation with dengue and COVID-19 was negligible. The results highlighted the serious underestimation of chikungunya mortality by epidemiological surveillance. We estimate that there were 890 excess deaths in the 2023 chikungunya epidemic in just one affected area of Minas Gerais, Brazil (2.5 million inhabitants). During the same year, only 420 chikungunya deaths were reported by all PAHO member countries. Epidemiological surveillance has underestimated the impact of this disease. Excess mortality is a crucial measure for understanding the impact of epidemics, as demonstrated by COVID-19 and influenza pandemics. The study highlights the need for complementary tools to traditional surveillance to better assess impacts on morbidity and mortality. Underreporting of chikungunya deaths has significant implications for public health responses and resource allocation. This study supports the importance of accurately quantifying mortality from emerging viruses to inform risk assessments and priority setting in public health interventions.