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Abstract
Legionellae are opportunistic bacterial pathogens causing Legionnaires’ disease and Pontiac fever and are ubiquitous in surface waters and in infrastructure to contain or distribute water, including pipes, cooling towers, and whirlpool spas. Infection in community-acquired and nosocomial outbreaks is by exposure to contaminated aerosols. Little is known about the presence of legionellae in groundwater. This study used samples from various locations in the United States and Canada to determine if legionellae could be isolated from water and biofilms derived from groundwaters not known to be under the direct influence of surface water. Of the 114 total samples of water and biofilm tested, 29.1% and 28.2% were positive for Legionella by cultivation and polymerase chain reaction (PCR), respectively. Legionellae were found in both warm and colder groundwaters, with more isolates from samples incubated at 30°C than the 35°C conventional temperature for Legionella isolation. The concentration of Legionella found in the water samples ranged from 102 to 105 CFU/L and up to 1.2 × 102 CFU/cm2 in the biofilm. The species of Legionella identified included both known pathogenic species and species that have not yet been identified as human pathogens. Millions of people in Canada, and around the world, rely on groundwater as their source for drinking. This study shows that legionellae are widespread in groundwater and have the potential to seed derived water supplies and biofilms in public distribution systems. This further widens the known sphere of Legionella colonization and the implications of its presence for public health.
Funding for this study was provided by the American Water Works Association Research Foundation (AWWARF). We are indebted to Professor Marilyn Lee for the protozoan analysis. The participation of the water utilities that provided samples for this study is also gratefully acknowledged.
Current addresses are: for Teresa Brooks, Health Canada, Water Quality and Health Bureau, Ottawa, Ontario, Canada; for Reagan A. Osicki, Saskatoon, Saskatchewan, Canada; and for Serge Riffard, Inst. Universitaire et Technologique de Saint Etienne, Génie Biologique–Génie de l'Environnement, St. Etienne Cédex, France.