Abstract Background The rapid spread and increase of chikungunya (CHIKV) and dengue (DENV) cases in Brazilian regions in 2023 has raised concerns about the impact of arboviruses on public health. Epidemiological and genomic surveillance was performed to estimate the introduction and spread of CHIKV and DENV in Brazil. Methods This study obtained results from the Hermes Pardini (HP), a private medical laboratory, and the Health Department of Minas Gerais state (SES-MG). We investigated the positivity rates of CHIKV and DENV by analyzing the results of 139,457 samples tested for CHIKV (44,029 in 2022 and 95,428 in 2023) and 491,528 samples tested for DENV (163,674 in 2022 and 327,854 in 2023) across the five representative geographical regions of Brazil. Genome sequencing was performed on 80 CHIKV and 153 DENV samples that had been positive for RT-PCR tests. Results In our sampling, the data from CHIKV tests indicated that the Northeast region had the highest regional positivity rate in 2022 (58.1%). However, in 2023, the Southeast region recorded the highest positivity rate (40.5%). With regard to DENV, the South region exhibited the highest regional positivity rate in both 2022 (40.8%) and 2023 (22.7%), followed by the Southeast region in both years (34.8% in 2022; 21.4% in 2023). During the first 30 epidemiological weeks of 2023 in the state of Minas Gerais (MG), there was a 5.8-fold increase in CHIKV cases and a 3.5-fold increase in DENV compared to the same period in 2022. Analysis of 151 new DENV-1 and 80 CHIKV genomes revealed the presence of three main clusters of CHIKV and circulation of several DENV lineages in MG. All CHIKV clades are closely related to genomes from previous Brazilian outbreaks in the Northeast, suggesting importation events from this region to MG. We detected the RNA of both viruses in approximately 12.75% of the confirmed positive cases, suggesting an increase of co-infection with DENV and CHIKV during the period of analysis. Conclusions These high rates of re-emergence and co-infection with both arboviruses provide useful data for implementing control measures of Aedes vectors and the urgent implementation of public health politics to reduce the numbers of CHIKV and DENV cases in the country.
