COVID-19 como evento disruptivo na ecologia viral: repercussões para as síndromes respiratórias agudas graves e para a interpretação das sequelas pós-infecciosas

Abstract

The COVID-19 pandemic acted as a disruptive event in respiratory viral ecology, reshaping seasonality, co-circulation patterns, and the clinical interpretation of acute respiratory syndromes and their post-infectious sequelae. This thesis integrates evidence from three complementary approaches addressing distinct phases and consequences of the pandemic in Minas Gerais, Brazil. During the pandemic phase (February to September 2021), a retrospective study in the Zona da Mata region analyzed respiratory samples processed by the molecular diagnostics service at ICB/UFJF, combining genomic surveillance (whole-genome sequencing) to characterize SARS-CoV-2 variants with molecular screening for other major respiratory viruses (human rhinovirus [HRV], respiratory syncytial virus [RSV], and influenza A/B), alongside clinical–epidemiological analyses and statistical modeling. In this period, the Gamma variant predominated and was associated with greater clinical severity compared with Delta (OR ~3.0; 95% CI: 1.21–7.32), with evidence of reduced influenza and RSV circulation during peaks of COVID-19 activity. Comorbidities such as diabetes (OR 2.14; 95% CI: 1.21–3.79) and obesity (OR 7.02; 95% CI: 1.49–33.00) were associated with SARS-CoV-2 infection, and heart disease showed an independent association with Gamma infection (aOR 3.54; 95% CI: 1.99–6.29). In the post-pandemic period (2023–2024), a second retrospective study evaluated severe acute respiratory illness cases (SRAG/SARI) from the Barbacena and Leopoldina regions processed at the SES/MG collaborating center at ICB/UFJF, integrating RT-qPCR (including multiplex assays) with clinical and epidemiological data. Among 264 samples from 36 municipalities, most cases were from urban residents (90.77%), with a heterogeneous age distribution (median 14 years). RSV (14.77%), HRV (11.36%), influenza A/B (9.46%), and SARS-CoV-2 (7.95%) were detected, while coinfections were uncommon (2.65%). A high proportion of SRAG/SARI cases remained without an identified viral etiology (53.78%), underscoring persistent diagnostic gaps despite expanded molecular testing capacity. Temporal patterns were atypical for influenza (peak in August 2024) and indicated a substantial RSVrelated hospitalization burden (increase from March to June 2024, peaking in May), whereas SARS-CoV-2 circulation was more sporadic. Across both phases, multivariate analyses support that clinical overlap among respiratory viruses remains a major barrier to syndromic management, and viral coinfections were not consistently associated with worse outcomes in the studied settings. Finally, a narrative synthesis discusses long COVID as a multisystem postinfectious condition characterized by heterogeneous definitions, lack of biomarkers, and significant impacts on quality of life and healthcare systems, exacerbated by misinformation, stigma, and inequalities in access to care. Overall, the findings reinforce the need for sustained, integrated respiratory virus surveillance beyond SARS-CoV-2, broader access to multiplex molecular diagnostics, strengthened vaccination strategies, and coordinated public health approaches that connect laboratory evidence, clinical decision-making, and preparedness for future respiratory health emergencies.