Health authorities suspect that dust from a nearby construction site could have contaminated the towers. Clive Broadbent has been hired to conduct an inspection. You may remember from the last issue of Legionella E-news that a food display humidifier was the focus of the investigation of this outbreak. Evidence suggests that the humidifier was indeed the source of contamination, because the strain of Legionella pneumophila serogroup 1 found in the two patients who died from Legionnaires' disease was indistinguishable from isolates found in the food display humidifier. The humidifier was used to produce mist over food in a refrigerated display unit.
Gas heaters benefit from the location of their heat source below the water tank.
Thus, the bottom of the tank, where sediment accumulates, is sufficiently hot to prevent legionellae growth. In addition, electric water heaters tend to have lower temperatures than do gas heaters. Alary M. and J.R. Joly. Risk factors for contamination of domestic hot water systems for Legionella. Lee, T.C., J.E. Stout, V.L. Yu.