Drs Stout and Yu have raised several important points about measures to eradicate legionellae from hospital water distribution systems.
The Hospital Infection Control Practices Advisory Committee recommends flushing each distal outlet on the water distribution system for at least 5 minutes with water 65°C or chlorinated to a level of 10 mg/L.1 It is likely that a longer duration of flushing will be more effective in reducing the concentration of organisms recovered from water samples.
However, difficulties in maintaining water pressure and temperature limit the feasibility of performing concurrent hot water flushes in more than a limited number of sites for longer than 5 to 10 minutes in some hospitals. Data from an experimental model suggest that heating water colonized with Legionella pneumophila to 66°C should lead to sterilization in less than 2 minutes.2
Although legionellae are relatively chlorine-resistant, maintenance of free residual chlorine levels at 1 to
Fiore AE, Kool JL, Carpenter J, Butler JC. Eradicating Legionella From Hospital Water-Reply. JAMA. 1997;278(17):1404-1405. doi:10.1001/jama.1997.03550170034025