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

Abstract

ENGLISH ABSTRACT: Legionella is a genus of pathogenic bacterial mesophiles that cause a range of diseases collectively referred to as Legionellosis, with immunocompromised 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 heated water temperatures allow Legionella to ourish. This paper uses computational uid dynamics modelling to show that the pipes downstream of a horizontal electric water heater provide an environment that is conducive to Legionella growth, not the heater itself. The presence of Legionella in water heaters is established through water sampled from ve in- eld water heaters, of which the temperatures and heating schedules are known. Microbiological techniques (PCR and weight-based qRT-PCR) are used to assess Legionella and L. pneumophila presence 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 middleincome countries, like South Africa, misdiagnosis of Legionellosis may be common due to the shadow cast by HIV and TB prevalence.