Assessing the role of ventilation and indoor air quality in SARS-CoV-2 transmission risk in Belgian nursing homes: the AIR-CO study

Indoor air quality (IAQ) and ventilation are important factors influencing the transmission of airborne respiratory viruses such as SARS-CoV-2. However, limited evidence exists on ventilation characteristics and IAQ in nursing homes (NHs), where residents are particularly vulnerable to infection. The COVID-19 pandemic highlighted the need for improved evidence to inform ventilation strategies in long-term care settings. This pilot environmental observational study aimed to assess IAQ and ventilation characteristics in Belgian NHs during the COVID-19 pandemic and to describe environmental SARS-CoV-2 detection alongside these conditions. Between January and May 2022, eleven NHs in Flanders were included. In each facility, five rooms ( n = 55 rooms in total), covering resident rooms, staff areas, and common spaces, were monitored for one week. Continuous measurements of carbon dioxide (CO₂), particulate matter (PM2.5), indoor temperature, and relative humidity (RH) were collected. In addition, one air sample and three surface swabs per room were analysed for SARS-CoV-2 RNA using RT-qPCR. Data were complemented with questionnaires, field observations, and staff interviews regarding ventilation systems and infection prevention and control practices. Nine facilities used fully mechanical ventilation (Type D), one combined natural supply with mechanical exhaust (Type C), and one relied on natural ventilation (Type A). CO₂ concentrations generally remained within recommended limits, particularly in mechanically ventilated rooms. RH values were consistently below seasonal recommended ranges, while indoor temperatures often exceeded recommended thresholds in resident rooms and common areas. PM2.5 levels were comparable across ventilation types, with higher values observed in some naturally ventilated spaces. Overall, 61.9% of surface swabs and 27.5% of air samples tested positive for SARS-CoV-2. Positive detections were most frequent during active or recent outbreaks, although no consistent association was observed between environmental viral detection and IAQ parameters. This pilot study provides an exploratory overview of IAQ, ventilation characteristics, and environmental SARS-CoV-2 detection in NHs. Although limited by sample size and heterogeneity, the study contributes integrated real-world data from long-term care settings. Future studies should include larger samples, detailed ventilation characterisation, and systematic monitoring of occupancy, activity patterns, and outdoor air conditions to better understand the relationship between ventilation, IAQ, and infection risk.