How to validate UV-C based air cleaners using viruses containing aerosols in a test room

UV-C based air cleaners may reduce the transmission of infectious diseases. However, microbiological validation is necessary to quantify their efficiency. In this study, the stability of aerosolized bacteriophages for validation purposes was investigated in a test room, before a UV-C based air cleaner was exemplarily evaluated regarding the inactivation of airborne bacteriophages.

The bacteriophage Phi6 was selected as virus surrogate and aerosolized in a room of 30 m³ volume. The recovery of infectious bacteriophages was first analyzed under variation of the relative humidity (20%-55% RH) and sampling time. The aerosol studies showed that a low humidity between 20% RH and 30% RH provides a high and stable recovery of bacteriophages Phi6 over 1 h. However, with increasing humidity, the number of infectious airborne bacteriophages Phi6 decreased significantly. At 50% RH, the recovery of Phi6 was 4 orders of magnitude lower compared to 20% RH. The validation of a UV-C based air cleaner was then demonstrated in the test room whereat the decline of infectious airborne bacteriophages was recorded over time. The nonenveloped bacteriophage MS2 was used as a reference. The validation results were significantly different for Phi6 when the humidity in the test room was either 40% RH or 30% RH, whereas comparable results were obtained for MS2 at both humidities.

A rising humidity in the test room caused a significant decline in the recovery of infectious airborne bacteriophages Phi6. The result of a quantitative validation of UV-C based air cleaners may therefore be affected by the respective humidity.