Cold traps as reliable devices for quantitative determination of SARS-CoV-2 load in aerosols

Spread of the severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) is a demanding challenge. This is of particular importance in schools and public areas of unavoidable access. New viral mutations may increase infectivity and require even better methods to identify areas of potential hazards. High-throughput SARS-CoV-2 testing and legal restrictions are not effective in order to get the current outbreak under control. The occurrence of new SARS-CoV-2 variants with a higher transmissibility requires efficient strategies for early detection and surveillance. Until today, testing focuses on nasal or pharyngeal mucosa swabs, neglecting the origin of aerosolic transmission, thus failing to detect the spread by carriers of the virus. Therefore, in this study, SARS-CoV-2 RNA levels were determined by quantitative real time PCR in aerosols collected by non-powered cold traps. SARS-CoV-2 spreading kinetics were recorded in indoor hotspots within a high-endemic area. These hotspots included a SARS-CoV-2 isolation unit, an outpatient endoscopy facility, a concert hall, and a shopping mall. For determination of viral presence aerosols were collected by cold traps positioned at different locations in the area of interest over a period of 4-6 h. Indoor SARS-CoV-2 hotspots were found in non-ventilated areas and in zones that are predisposed to a buoyancy (chimney) effect. SARS-CoV-2 RNA in those aerosols reached concentrations of 10⁵ copies/mL, while extensive outdoor air ventilation reliably eliminated SARS-CoV-2 aerosol contamination. The method presented herein is effective for the identification of SARS-CoV-2 indoor hotspots and may help to characterize the spreading kinetics of SARS-CoV-2. Moreover, it can be used for the surveillance of emerging SARS-CoV-2 variants. Due to low costs and easy handling, the procedure might enable efficient algorithms for COVID-19 screening and prevention.