Study population and setting
Investigators collected 56 samples from three different air handling units (AHUs) at the Oregon Health and Science University Hospital in May and June 2020 to determine the presence of SARS-CoV-2 RNA. These AHUs were located in different parts of the building. Data collectors sampled pre-filters, final filters, and supply dampers and recorded the direction of air flow for the vents. The air units both collect air from outside air flow and recirculate air to multiple floors of the hospital. Data collectors sampled surfaces from both the return and supply air parts of the AHUs.
Summary of Main Findings
SARS-CoV-2 RNA was present in 14 out of 56 (25%) of the samples collected. RNA was found in 7 out of the 20 pre-filters (35%), 2 out of the 12 final filters (17%), and 5 out of the 24 supply air dampers (21%). The HVAC system cycles from the ward to the AHU and back to the ward between 90 seconds and five minutes. Though, investigators detected viral RNA among the samples, it is unknown if these were viable particles (i.e. able to cause infection if inhaled).
This study provides valuable information concerning the possibility of aerosolized transmission through ventilation systems.
The study did not test for live viral particles of SARS-CoV-2 and thus it is not clear whether the particles found were viable to infect people. Furthermore, investigators were not able to perform sampling on a regulated schedule so that they would not interrupt hospital operations. Investigators also did not collect samples of the air flowing in and out of the AHUs in addition to sampling the surfaces on the AHUs.
This is one of the first studies to examine the presence of SARS-CoV-RNA in air handling units. The fact that investigators found the presence of viral RNA in the samples suggest potential transmission through ventilation systems. Since these AHUs recirculate are throughout multiple rooms in the building, people may be vulnerable to infection even if they are not in the same room as someone infected if the aerosolized viral particles are still viable once circulated through the AHUs.
This review was posted on: 19 August 2020