Author Identifiers

Edmore Masaka

https://orcid.org/0000-0001-5052-5479

Date of Award

2021

Degree Type

Thesis

Degree Name

Doctor of Philosophy

School

School of Medical and Health Sciences

First Advisor

Sue Reed

Second Advisor

Jacques Oosthuizen

Third Advisor

Maggie Davidson

Abstract

Water mist systems (WMS) installed and used for cooling ambient temperatures in public places fall within the category of premise plumbing. Premise plumbing refers to the water distribution networks that lie downstream of the water meter, and within buildings. The colonization of premise plumbing by opportunistic premise plumbing pathogens (OPPPs) such as Legionella pneumophila, Pseudomonas aeruginosa, Mycobacterium avium, Acanthamoeba and Naegleria fowleri is emerging as a challenge for public health and water quality management. Contrary to other premise plumbing features like showers and domestic taps that have been implicated in various waterborne infections, the health risks associated with WMS are not well understood.

The primary aim of this thesis research was to advance understanding of the health risks associated with OPPPs in WMS used to cool ambient air temperatures for thermal comfort. A literature review was the foundation (1st study) of this research and aimed to characterise the state of knowledge about the health risks of OPPPs in WMS. The 2nd study, a questionnaire survey of 10 WMS owners and 22 Environmental Health Officers (EHOs) was conducted as formative research to understand and describe the characteristic features of WMS, as well as the knowledge, perspectives and practices of operators, and regulatory authorities that manage these systems within the context of public health legislation. Additionally, this formative research informed the research methodology for the 3rd study, a microbial investigation of 10 WMS, from which 30 bioaerosol (air), biofilm (surface) and water samples were collected, giving a total of ninety samples (N=90). Microbial samples were analysed by both culture-based (growth media) and culture-independent (polymerase chain reaction (PCR)) methods to quantify and identify the presence of 5 representative OPPPs: L. pneumophila, P. aeruginosa, M. avium and free-living amoebae (FLA) including Acanthamoeba and N. fowleri. Data on water profile parameters of water temperature, water pH and concentration of free residual chlorine, total dissolved solids (TDS) and total organic carbon (TOC) were statistically analysed to determine their impact on the colonisation of OPPP in WMS.

This research identified a critical knowledge gap regarding the health risk of OPPPs in WMS (Study 1), as well as low levels of awareness amongst WMS managers and EHO’s regarding the health risks associated with WMS including: non-existent or adhoc maintenance regimes, and lack of training and education about the systems (Study 2). Furthermore, the Study 3 research demonstrated colonisation of WMS by public health pathogens of concern including of P. aeruginosa (49%), L. pneumophila serogroup (Sg) 2-14 (18%) and L. pneumophila Sg 1 (6 %), and Acanthamoeba (< 3 %). On the positive, neither M. avium nor N. fowleri were detected in the WMSs investigated. Free residual chlorine was negatively correlated with all OPPPs, except for Acanthamoeba indicating that this may be a critical variable in the safe operation of WMS. L. pneumophila Sg 2-14 and Sg 1 were strongly correlated with both TDS and TOC concentration, indicating that these indicators could be used as a warning for at-risk systems, as could elevated water temperature that was positively correlated with P. aeruginosa.

This research indicates that WMS present a potential health risk due to colonisation by L. pneumophila Sg 2-14, L. pneumophila Sg 1, P. aeruginosa and Acanthamoeba, and should be regulated under public health legislation for microbial contamination of air handling and water systems. Consideration should be given to reviewing existing public health legislation to capture WMS used as a cooling intervention with consideration of other emerging OPPPs besides Legionella spp., as well as development of codes/guidelines for the auditing and operation of WMS, and the upskilling and training of operators and EHOs on their associated health risks. This research has practical applications in public health, as well as commercial WMS cleaning and maintenance businesses, and other industries that use WMS for air cooling and dust suppression.

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