SARS-CoV-2 surveillance in indoor and outdoor size-segregated aerosol samples.

We aimed to determine the presence of SARS-CoV-2 RNA in indoor and outdoor size-segregated aerosol samples (PM, PM). Five outdoor daily samples were collected between November and December 2020 in an urban/industrial area with relatively high PM levels (Maliaño, Santander, Spain) by using a PM impactor (air flowrate of 30 L/min). In a non-hospital indoor sampling surveillance context, 8 samples in classrooms and 6 samples in the central library-Paraninfo of the University of Cantabria (UC) were collected between April and June 2021 by using personal PM samplers (air flowrate of 3 L/min). Lastly, 8 samples in the pediatric nasopharyngeal testing room at Liencres Hospital, 6 samples from different single occupancy rooms of positive patients, and 2 samples in clinical areas of the COVID plant of the University Hospital Marqués de Valdecilla (HUMV) were collected between January and May 2021. N1, N2 genes were used to test the presence of SARS-CoV-2 RNA by RT-qPCR. SARS-CoV-2 positive detection was only obtained from one fine fraction (PM) sample, corresponding to one occupancy room, where a patient with positive PCR and cough was present. Negative results found in other sampling areas such as the pediatric nasopharyngeal testing rooms should be interpreted in terms of air sampling volume limitation and good ventilation.