Speaker
Description
Background/Objective
The transmission of SARS-CoV-2 through aerosols has been recognized as a critical pathway for infection, especially in indoor settings with limited ventilation, where people share spaces over extended periods. Despite its importance, during the COVID-19 pandemic period there was a notable scarcity of studies assessing the presence of SARS-CoV-2 genetic material in shared spaces frequented by vulnerable populations, such as elderly care homes and primary schools.
Elderly care homes are the residence of individuals with a heightened risk of severe COVID-19 outcomes due to age-related factors and underlying comorbidities. Primary schools involve young children who, although less likely to experience severe symptoms, may serve as vectors for virus transmission within their households and the broader community. Understanding the presence and concentration of SARS-CoV-2 in aerosols within these environments is crucial for the development of effective mitigation strategies.
This study aims to evaluate the presence and concentration of SARS-CoV-2 genetic material in aerosol samples collected in environments frequented by vulnerable groups, such as elderly care homes and primary schools within the Valencian Community, Spain.
Methods
Between March 2021 and July 2021, 175 aerosol samples were collected from 9 elderly care homes (n = 92) and 9 primary schools (n = 83) across the three provinces of the Valencian Community, Spain. No known cases of COVID-19 were present in the microenvironments at the time of sampling. Samples were collected in sterile 47 mm quartz fibre filters over 24-hour periods using Derenda low-volume samplers (2.3 m³/h) equipped with PM2.5 inlets. The samplers were strategically positioned within each sampling microenvironment to ensure representativeness, with the air inlet located 1 m above the ground and away from potential sources of interference, such as doors, windows, and air conditioning or mechanical ventilation units.
Mengovirus (MgV) was used as an internal control for the efficiency of genetic material extraction. Genetic material was extracted and analysed using RT-qPCR targeting the N1 nucleocapsid and E envelope genes. When positive, the viral load was quantified in genomic copies (gc)/m³.
Since concentrations are not normally distributed, medians and interquartile ranges (IQR) are reported. Differences in SARS-CoV-2 RNA detection rates between the two settings were evaluated using a Chi-square test. Associations between the type of environment and viral load were analysed with a Mann-Whitney U test.
Results
The mean recovery rate of the MgV internal control was 58 % ± 38 %. SARS-CoV-2 RNA was detected in 14 out of 175 samples (8%), with 11 positive samples in elderly care homes (12%) and 3 in primary schools (3.6%). Detection rates differed significantly between elderly care homes and primary schools (p < 0.05).
The viral RNA concentrations in elderly care homes were significantly higher than in primary schools (p < 0.01). Median concentrations in elderly care homes were 8.2 gc/m³ (IQR: 7.6 – 13.0, n=11), compared to 4.1 gc/m³ (IQR: 4.0 – 4.6, n=3) in primary schools. The maximum concentration observed in elderly care homes was 78 gc/m³, while the maximum in primary schools was 5.1 gc/m³.
Conclusion
This study confirms the presence of SARS-CoV-2 genetic material in the air of elderly care homes and primary schools, where no known cases of COVID-19 were present at the time of sampling. The findings reveal that the detection rate and concentrations of viral RNA in aerosols was significantly higher in elderly care homes compared to primary schools. These results highlight the critical need for targeted control measures in spaces frequented by vulnerable populations - such as enhanced ventilation and tailored prevention strategies- particularly in elderly care homes where viral loads were markedly elevated.
