Abstract Rationale Clinical conditions such as asthma, COPD, allergic diseases and immunodeficiencies represent major risk factors (RF) for upper and lower respiratory tract infections (RTIs). Furthermore, RTIs are often triggers for chronic obstructive lung disease exacerbations. There are conflicting results on a changed incidence of RTIs after COVID-19. This is an independent multicentric 2-year prospective observational study aimed at assessing the actual incidence of RTIs in a large adult population with and without risk factors (RF and noRF) for RTIs. (SIRTI - clinicaltrials.gov NCT06649032). Methods A total of 1726 subjects (608 noRF and 1118 RF, including 657 with asthma and 238 with COPD) were recruited across two consecutive years and monitored for the incidence of RTIs over 4-months during the Winter-Spring season. Subjects experiencing at least one RTI within the observational period were followed-up for additional 12 months. Results The number of RTIs along the monitored period in the study population (primary outcome) was 785 (0.5+/-0.7 per subject), 240 in subjects noRF and 545 in subjects RF (p = 0.02). The occurrence of RTIs caused 103 exacerbations of asthma and 27 of COPD. Type, severity and time to first respiratory infection, as well as vaccinations and antibiotic use were also recorded. A significant (p 0.01) difference in the incidence of RTIs was observed between subjects recruited in the first year (2024 - 0.5+/-0.7) compared to those enrolled in the second year (2025 - 0.4+/-0.6). Subjects with at least one RTI during the 4-month observation period (33%) showed a higher susceptibility for RTIs in the following 12 months and/or in the 3 years before recruitment. Conclusions The incidence of RTIs is confirmed to be high, particularly in subjects with risk factors, despite resulting lower than that reported before COVID-19, and variable from year to year. Even one RTI during the Winter/Spring period is highly predictive of a susceptibility to recurrent RTI. The actual incidence of RTIs should be taken into account, when defining frequent asthma and COPD exacerbators, for clinical trial designs, guideline definitions and regulatory body decisions. This abstract is funded by: N/A
Bonini et al. (Fri,) studied this question.