Bacteriophage aerosol challenge of installed air contamination control systems

Control technologies to prevent aerosol-based disease transmission in animal agriculture production settings: a review of established and emerging approaches

Transmission of infectious agents via aerosols is an ever-present concern in animal agriculture production settings, as the aerosol route to disease transmission can lead to difficult-to-control and costly diseases, such as porcine respiratory and reproductive syndrome virus and influenza A virus. It is increasingly necessary to implement control technologies to mitigate aerosol-based disease transmission. Here, we review currently utilized and prospective future aerosol control technologies to collect and potentially inactivate pathogens in aerosols, with an emphasis on technologies that can be incorporated into mechanically driven (forced air) ventilation systems to prevent aerosol-based disease spread from facility to facility. Broadly, we find that control technologies can be grouped into three categories: (1) currently implemented technologies; (2) scaled technologies used in industrial and medical settings; and (3) emerging technologies. Category (1) solely consists of fibrous filter media, which have been demonstrated to reduce the spread of PRRSV between swine production facilities. We review the mechanisms by which filters function and are rated (minimum efficiency reporting values). Category (2) consists of electrostatic precipitators (ESPs), used industrially to collect aerosol particles in higher flow rate systems, and ultraviolet C (UV-C) systems, used in medical settings to inactivate pathogens. Finally, category (3) consists of a variety of technologies, including ionization-based systems, microwaves, and those generating reactive oxygen species, often with the goal of pathogen inactivation in aerosols. As such technologies are typically first tested through varied means at the laboratory scale, we additionally review control technology testing techniques at various stages of development, from laboratory studies to field demonstration, and in doing so, suggest uniform testing and report standards are needed. Testing standards should consider the cost-benefit of implementing the technologies applicable to the livestock species of interest. Finally, we examine economic models for implementing aerosol control technologies, defining the collected infectious particles per unit energy demand.

Efficacy of single pass UVC air treatment for the inactivation of coronavirus, MS2 coliphage and Staphylococcus aureus bioaerosols

There is strong evidence that SARS-CoV-2 is spread predominantly by airborne transmission, with high viral loads released into the air as respiratory droplets and aerosols from the infected subject. The spread and persistence of SARS-CoV-2 in diverse indoor environments reinforces the urgent need to supplement distancing and PPE based approaches with effective engineering measures for microbial decontamination - thereby addressing the significant risk posed by aerosols. We hypothesized that a portable, single-pass UVC air treatment device (air flow 1254 L/min) could effectively inactivate bioaerosols containing bacterial and viral indicator organisms, and coronavirus without reliance on filtration technology, at reasonable scale. Robust experiments demonstrated UVC dose dependent inactivation of Staphylococcus aureus (UV rate constant (k) = 0.098 m²/J) and bacteriophage MS2, with up to 6-log MS2 reduction achieved in a single pass through the system (k = 0.119 m²/J). The inclusion of a PTFE diffuse reflector increased the effective UVC dose by up to 34% in comparison to a standard Al foil reflector (with identical lamp output), resulting in significant additional pathogen inactivation (1-log S. aureus and MS2, p < 0.001). Complete inactivation of bovine coronavirus bioaerosols was demonstrated through tissue culture infectivity (2.4-log reduction) and RT-qPCR analysis - confirming single pass UVC treatment to effectively deactivate coronavirus to the limit of detection of the culture-based method. Scenario-based modelling was used to investigate the reduction in risk of airborne person-to-person transmission based upon a single infected subject within the small room. Use of the system providing 5 air changes per hour was shown to significantly reduce airborne viral load and maintain low numbers of RNA copies when the infected subject remained in the room, reducing the risk of airborne pathogen transmission to other room users. We conclude that the application of single-pass UVC systems (without reliance on HEPA filtration) could play a critical role in reducing the risk of airborne pathogen transfer, including SARS-CoV2, in locations where adequate fresh air ventilation cannot be implemented.

Direct and quantitative capture of viable bacteriophages from experimentally contaminated indoor air: A model for the study of airborne vertebrate viruses including SARS-CoV-2

Aim

The air indoors has profound health implications as it can expose us to pathogens, allergens and particulates either directly or via contaminated surfaces. There is, therefore, an upsurge in marketing of air decontamination technologies, but with no proper validation of their claims. We addressed the gap through the construction and use of a versatile room‐sized (25 m³) chamber to study airborne pathogen survival and inactivation.

Methods and Results

Here, we report on the quantitative recovery and detection of an enveloped (Phi6) and a non‐enveloped bacteriophage (MS2). The two phages, respectively, acted as surrogates for airborne human pathogenic enveloped (e.g., influenza, Ebola and coronavirus SARS‐CoV‐2) and non‐enveloped (e.g., norovirus) viruses from indoor air deposited directly on the lawns of their respective host bacteria using a programmable slit‐to‐agar air sampler. Using this technique, two different devices based on HEPA filtration and UV light were tested for their ability to decontaminate indoor air. This safe, relatively simple and inexpensive procedure augments the use of phages as surrogates for the study of airborne human and animal pathogenic viruses.

Conclusions

This simple, safe and relatively inexpensive method of direct recovery and quantitative detection of viable airborne phage particles can greatly enhance their applicattion as surrogates for the study of vertebrate virus survival in indoor air and assessment of technologies for their decontamination.

Significance and Impact of the Study

The safe, economical and simple technique reported here can be applied widely to investigate the role of indoor air for virus survival and transmission and also to assess the potential of air decontaminating technologies.

T1 bacteriophage as an indicator for decontamination of laminar-flow biological safety cabinets

Type 1 coliphage dried onto a glass surface was used as an indicator to monitor decontamination of biological safety cabinets. When desiccated virus was treated with formaldehyde vapor (5,000 or 10,000 ppm) adjusted to 70 to 90% relative humidity immediately before testing, viral inactivation was slow for the first 50 min but then accelerated, being complete in the next 10 min. However, when virus was incubated in an atmosphere containing 70% humidity for 1 h before formaldehyde was added, inactivation was complete within 3 min, indicating that careful attention must be paid to relative humidity in decontamination of safety cabinets.

Evaluation of a commercial air filter for removal of viruses from the air

The effectiveness of a commercial absolute air filter for removal of viruses from air was tested with an actinophage, under the usual conditions of a laminar airflow clean room. A new method of dry phage dispersion is described. The filter showed an average reduction of 99.996% of airborne actinophage.