To assess risk factors associated with the contamination of the domestic environment by legionellae, 211 houses in the Quebec City area were randomly selected and water samples were collected from the hot water

tank, the shower heads, and the most frequently used faucet. After centrifugation, concentrated samples were

seeded in triplicate on BCYE and GPV media. Data on the characteristics of the hot water system and plumbing

in the house and on the personal habits of the occupants were collected for each house. Among these 211 houses,

hot water was provided by either an oil or gas heater in 33 and by an electric heater in 178. Legionellae were

isolated from none of the samples from houses with oil or gas heaters and from 39% (69 of 178) of those with

electric water heaters (P < 0.0001). This association remained highly significant after control for water

temperature and other variables in a stratified analysis. In the 178 houses with an electric heater, 12% of the

faucets, 15% of the shower heads, and 37% of the water heaters were contaminated. Legionella pneumophila

serogroups 2 and 4 were the most frequently isolated strains. Logistic regression showed that factors associated

with electric water heater contamination were (i) location of the house in older districts of the city (P < 0.0001),

(ii) old age of the water heater (P = 0.003), and (iii) low water temperature (P = 0.05). Contamination of the

water heater was the only factor significantly associated with the contamination of peripheral outlets (P <

0.0001). This study shows that the presence of an electric heater is strongly associated with contamination of

domestic hot water systems by Legionellae. The public health importance of this contamination is still

unknown.

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View Journal Article https://journals.asm.org/doi/epdf/10.1128/aem.57.8.2360-2367.1991

Original Post https://doi.org/10.1128/aem.57.8.2360-2367.1991

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