Factors Influencing Legionella Contamination of Domestic Household Showers

Abstract

Legionnaires' disease is a potentially fatal pneumonia like infection caused by inhalation or aspiration of water particles contaminated with pathogenic Legionella spp. Household showers have been identified as a potential source of sporadic, community-acquired Legionnaires' disease. This study used qPCR to enumerate Legionella spp. and Legionella pneumophila in water samples collected from domestic showers across metropolitan Adelaide, South Australia. A survey was used to identify risk factors associated with contamination and to examine awareness of Legionella control in the home. The hot water temperature was also measured. A total of 74.6% (50/68) and 64.2% (43/68) showers were positive for Legionella spp. and L. pneumophila, respectively. Statistically significant associations were found between Legionella spp. concentration and maximum hot water temperature (p = 0.000), frequency of shower use (p = 0.000) and age of house (p = 0.037). Lower Legionella spp. concentrations were associated with higher hot water temperatures, showers used at least every week and houses less than 5 years old. However, examination of risk factors associated with L. pneumophila found that there were no statistically significant associations (p > 0.05) with L. pneumophila concentrations and temperature, type of hot water system, age of system, age of house or frequency of use. This study demonstrated that domestic showers were frequently colonized by Legionella spp. and L. pneumophila and should be considered a potential source of sporadic Legionnaires' disease. Increasing hot water temperature and running showers every week to enable water sitting in pipes to be replenished by the municipal water supply were identified as strategies to reduce the risk of Legionella in showers. The lack of public awareness in this study identified the need for public health campaigns to inform vulnerable populations of the steps they can take to reduce the risk of Legionella contamination and exposure.

Keywords: Legionella pneumophila; Legionnaires’ disease; opportunistic pathogens; potable water; public health; water quality.

Figure 1

Scatter plot showing the set hot water temperature (°C) and Legionella spp. (copies/mL) on log₁₀ scale with loess line of fit.

Figure 2

Boxplot showing mean concentration of Legionella spp. (copies/mL) on a log₁₀ scale by the age of the house (determined by survey responses).

Figure 3

Boxplot showing mean concentration of Legionella spp. (copies/mL) on a log₁₀ scale by the frequency of shower use (determined by survey responses).