Aerosolization of Microbial Pathogens and Indicator to Assess their Transport and Dispersion in Air

“Airborne dispersal of microorganisms influences their biogeography, gene flow, atmospheric processes, human health and transmission of pathogens that affect humans, plants and animals” (Alsved et al., 2018). Many airborne pathogens cause diseases, such as Legionnaires disease, which is a type of pneumonia caused due to Legionella. Since the first report of a Legionella outbreak in 1976, or reports of Non – tuberculous Mycobacterium (NTM) outbreaks in hospital and healthcare settings by the CDC, it is significant to understand the behavior, occurrence and persistence of opportunistic pathogenic aerosols in the atmosphere. This study comprises a literature review and experimental work on airborne dispersion of 4 microorganisms – E. coli, Legionella pneumophila, Mycobacterium phlei and bacteriophage P22. The literature review summarizes their characteristics, their potential sources, disease outbreaks, collection and detection methodologies, environmental conditions for their growth and survival and few recommendations for reducing potential outbreaks. Aerosolization of each of these microorganisms was carried out separately in a closed environment using a spray gun and a nebulizer. The spraying time consisted of 1 sec, 5secs or 10secs, from one end of a chamber, and collecting air sample from the other end of the chamber, using a microbial air sampler. The air sample collection was performed to understand their transport, dispersion and reduction in air. Legionella showed a log reduction of ~4 using spray gun and ≤0.6 using nebulizer, whereas Mycobacterium showed a log reduction of ~4.5 using spray gun and ≤0.7 using nebulizer, respectively. Bacteriophage P22 on the other hand showed a 4 log reduction using spray gun and ≤1.4 using the nebulizer. This shows that aerosolization of microorganisms depends on its cell structure, size and survivability. Legionella follows the air – to – water transmission route, and Mycobacterium is hydrophobic, due to which their aerosols are more stable and active, than E. coli. Other environmental properties such as relative humidity and temperature impact the transport and dispersion of microorganisms in air.

The experiments in this study validated the aerosolization and transport of Legionella, Mycobacterium and bacteriophage P22 in a closed environment over time. In general, microbial concentration collected in air increased with aerosolization time of the test water. On the other hand, their concentration significantly decreased as elapsed time progressed after aerosolization, due to settling effect of larger particles and potential reduction due to inactivation of bacterial and viruses in the air.