Guest: Dr Jo Barnes is a senior lecturer in Community Health at Stellenbosch University's Faculty of Health Sciences.

In South Africa, there is no information about the prevalence of Legionella in domestic
water heaters, which normally heat water to 65°C. However many users keep
temperatures as low as 40°C in a compromise between being more financially savvy
and still enjoying a satisfactory water temperature. This is the perfect environment for
the growth of Legionella which thrives at temperatures from 37 to 42°C.

To determine the presence of Legionella, the researchers cut open water heaters
shortly after they had failed mechanically and collected samples and biofilm scrapings
from inside the heaters. They also separately used microbiological techniques to assess
the presence of Legionella at the point-of-use in the tap water from five active heaters,
which they compared to cold water from the same source as a control.

According to the findings in the study, the bacterial concentrations in the plumbing
between the water heater and the taps were as much of a concern as those in the
heater tank.

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