Since its first report in 1976, many outbreaks linked to Legionella have been reported in the world. These outbreaks are a public health concern because of legionellosis, which is found in two forms, Pontiac fever and Legionnaires disease. Legionnaires disease is a type of pneumonia responsible for the majority of the illness in the reported outbreaks of legionellosis. This study consists of an extensive literature review and experimental work on the aerosolization and UV inactivation of E.coli and Legionella under laboratory conditions. The literature review summarizes Legionella general information, occurrence, environmental conditions for its survival, transmission to human, collection and detection methodologies and Legionella disinfection in air and during water treatment processes.
E. coli was used as an surrogate for Legionella in experimentation due to their similar bacterial properties such as size, gram-negative rod-shaped, un-encapsulated and non-spore-forming bacterial cells. The accessibility and non-pathogenicity of E. coli also served as factors for the substitution.
Three methods of bacterial aerosolization were examined, these included an electric spray gun, an air spray gun and a hand-held spray bottle. A set of experiments were performed to examine E. coli aerosolization and transport in the aerosolization chamber (an air tight box) placed in a Biological Safety Cabinet. Spiked sample was sprayed through the opening from one side of the aerosolization chamber using the selected aerosolization methods. The air sampler was placed at the other side to collect 100 L air sample from the aerosolization chamber. A Tryptic Soy Agar plate was placed inside the air sampler to collect and subsequently culture E. coli cells from air. Results showed that the air spray gun has the best capability of aerosolizing bacteria cells under all the conditions examined in this study compared to the other two spray methods. In this study, we provide a practical and efficient method of bacterial aerosolization technique for microbial dispersion in air. The suggested method can be used in future research for microbial dispersion and transmission studies.
A set of experiments were performed to examine UV inactivation of E. coli and Legionella cells in air. Spiked samples were sprayed through the opening from one side of the aerosolization chamber using the air spray gun. A UV-C germicidal lamp inside the Biological Safety Cabinet was turned on after each spray. The air samples were collected as previously described. The application of UV-C for the inactivation of bacterial cells resulted in removing aerosolized E. coli and Legionella cells in air. A 1 log reduction was achieved with 5 seconds UV exposure time while 10 seconds UV exposure resulted in a 2 log bacterial reduction for both bacteria. This study shows the applicability of UV inactivation of pathogenic bacterial cells in air by short UV exposure time. This method may be applicable for the inactivation of Legionella in air ducts by installing germicidal UV lamps for protecting susceptible populations in certain indoor settings such as nursing homes or other community rooms.