A potential source of undiagnosed Legionellosis: Legionella growth in domestic water heating systems in South Africa

Abstract Legionella is a genus of pathogenic bacterial mesophiles that cause a range of diseases collectively referred to as Legionellosis, with immuno-compromised individuals being particularly susceptible. Water heaters, a potential domestic niche for these pathogens, are heavy energy consumers, causing cost-sensitive users to employ energy-saving initiatives, such as scheduling and lower temperature set points. However, lower water temperatures allow Legionella to flourish. This paper uses computational fluid dynamics modelling to show that a horizontal electric water heater provides an environment that is conducive to Legionella growth, although its prevalence is probably higher in the downstream pipes. The presence of Legionella in water heaters is established through water sampled from five in-field water heaters, of which the temperatures and heating schedules are known. Microbiological techniques (PCR and weight-based qRT-PCR) are used to assess the presence of Legionella and L. pneumophila at point-of-use taps. A model is used to determine the potential infection rate from these concentrations, demonstrating that undiagnosed Legionellosis infection is likely. In low- and middle-income countries, like South Africa, misdiagnosis of Legionellosis may be common due to the shadow cast by HIV and TB prevalence.