Assessment of SARS-CoV-2 and other IAQ parameters in 11 Belgian elderly care homes

It is often difficult to implement prevention recommendations and plan targeted measures to limit the spread of airborne viruses in communal spaces. To effectively accomplish this goal, it is crucial to comprehensively characterize the indoor environmental quality in the space and, from these space-specific data, draw recommendations adapted to the setting. In this context, 11 elderly care homes in Belgium were selected for a comprehensive assessment of the indoor air quality (IAQ). IAQ and ventilation parameters were characterized by means of air sampling and questionnaire application. In each elderly care home, a survey on ventilation strategies and behaviour, building characteristics and COVID-19 prevention practices was applied, and 5 rooms were selected for IAQ measurements (2 resident bedrooms, at least one common room for residents, one staff room and one extra common room for residents or visitors). In each room, a set of IAQ parameters expected to be related to the indoor virus transmission (CO2, temperature and relative humidity in all rooms, plus PM2,5 in selected rooms) were continuously monitored with an in-house developed and calibrated sensor box for 7 days. Biological samples were collected from the air (via liquid impingement) and surfaces (via swipe sampling), once per room, for in-lab detection of SARS-CoV-2 RNA copies via RT-qPCR. Particulate matter (PM2,5) concentrations in all facilities were most of the time low, not exceeding the applicable PM2.5 indoor guideline value. CO2 concentrations generally indicated acceptable levels of ventilation in all facilities, with the lowest CO2-concentrations measured in mechanically ventilated ones. Of all collected air samples, 28% contained traces of SARS-CoV-2 RNA, while 63% of the swab samples did. The number of positive SARS-CoV-2 samples collected in each elderly care centre did not follow the trend of Flemish COVID-19 incidence rate during each respective sampling week. In the care homes where there was an on-going COVID-19 outbreak during measurements, all air samples and most of the surface samples tested positive for SARS-CoV-2. In the absence of a reported on-going local outbreak, positive SARS-CoV-2 samples were found mainly on surfaces. These results indicate that more than one positive SARS-CoV-2 air sample in one building might work as an indicator of an on-going outbreak (or at least of the presence of SARS-CoV-2 RNA emitters), which in the context of asymptomatic persons in this setting occupied by a vulnerable population is of high value. Furthermore, even though an indoor CO2 concentration below 900 ppm is often considered indication of lower risk of indoor virus transmission, the dominant variant at that time of the pandemic (delta) appeared in all SARS-CoV-2 positive air samples. Therefore it is recommended to initiate additional risk reduction strategies in case of a local outbreak, such as increasing ventilation rates, implementing effective air cleaning, using mouth masks and isolating infected persons (symptomatic or not), especially in sensitive settings like these.