PHAGES AS SURROGATES FOR PATHOGENIC VIRUSES IN ANALYSIS AND VALIDATION OF UV DISINFECTION AND THERMAL DISINFECTION PROCESSES FOR AIR AND SURFACES

Bacteriophage (phage) are viruses that infect bacterial cells. Phage have structural and physiological features that mimic viruses that are pathogenic to humans, but phage are unable to infect human cells. Therefore, phage are often used as surrogates for human viruses in studies of disinfection processes.

This research explored the intrinsic kinetics of inactivation of three bacteriophage as a result of UV-C exposure and elevated temperature. UV sensitivity of the phages T1, MS2, and F6 were demonstrated to be wavelength dependent. Thermal inactivation of MS2 and F6 was observed starting from a threshold value around 50°C.

Subsequent work allowed for characterization of bacteriophage as surrogates for pathogenic viruses by comparing their intrinsic kinetics of UV inactivation with those of viral pathogens, as well as comparing the structure and physiology of phages with pathogens. T1 was found to be a conservative surrogate for airborne phage such as influenza and SARS-CoV-2 for UV-C radiation. F6 was found to be extremely sensitive to Far UV-C radiation, possibly due the presence of a protein envelope.

Phage were then applied as challenge agents for testing and validation of in-room, UV-based air cleaners. Experiments were conducted to quantify the dynamic behavior of aerosolized phage in an indoor air quality (IAQ) chamber. A mathematical model was also developed to define these dynamics. Collectively, the experimental and numerical methods were presented as a protocol for quantification of the effects of UV-based air cleaners, and for translation of the results from the testing environment to the application environment.

Experiments were also conducted to quantify the behavior of UVC-based devices for disinfection of personal space. These devices represent alternatives to conventional filtering masks (e.g., N95), but allow for inactivation of aerosolized pathogens rather than relying on physical separation (i.e., filtration).

Lastly, experiments were conducted to define the wavelength-dependence (action spectra) of UV-based inactivation of viruses. A series of collimated UV sources was used to apply UV radiation from across the UV-C and UV-B portions of the electromagnetic spectrum to aqueous viral suspensions. Because the output of many of the collimated sources was polychromatic, an algorithm was developed to deconvolve the action spectrum from each viral data set. This approach provides a new method for quantification of microbial and viral action spectra; this approach will be important for quantification of action spectra for newly-discovered pathogens and for new sources of UV radiation.