Epidemiological and clinical profile of respiratory viral infections in 2021: integrated surveillance during the COVID-19 pandemic

Background The COVID-19 pandemic disrupted the seasonality and detection patterns of other respiratory viruses, complicating syndromic surveillance and clinical management in several regions, including Brazil.Objectives To describe the epidemiological, clinical and hospitalization profiles of patients with laboratory-confirmed respiratory viral infections diagnosed in 2021, comparing SARS-CoV-2 variants, influenza B, respiratory syncytial virus (RSV), human rhinovirus (HRV) and negative cases.Methods We conducted a retrospective analysis of molecular diagnostic results and clinical – epidemiological data from 337 patients/samples. Analyses included logistic regression to estimate odds ratios (ORs) for risk factors and principal component analysis (PCA) to explore symptom clustering.Findings SARS-CoV-2 (Gamma variant), HRV, RSV and influenza B were the most frequently detected viruses. PCA revealed virus-specific symptom clusters, with notable overlap among pathogens. Compared with Delta, Gamma showed higher clinical severity (OR ~ 3.0; CI95%: 1.21–7.32). Diabetes and obesity were significantly associated with COVID-19. Coinfections were infrequent and not linked to greater severity.Main conclusions Findings support integrated respiratory surveillance using multiplex PCR in sentinel settings, variant-aware clinical screening and timely genomic characterization to guide care pathways and inform local public health actions.