Legionella contamination of dental-unit waters

Abstract

Water samples collected from 28 dental facilities in six U.S. states were examined for the presence of Legionella pneumophila and other Legionella spp. by the PCR-gene probe, fluorescent-antibody microscopic, and viable-plate-count detection methods. The PCR and fluorescent-antibody detection methods, which detect both viable and viable nonculturable Legionella spp., gave higher counts and rates of detection than the plate count method. By the PCR-gene probe detection method, Legionella spp. were detected in 68% of the dental-unit water samples and L. pneumophila was detected in 8%. Concentrations of Legionella spp. in dental-unit water reached 1,000 organisms per ml or more in 36% of the samples, and 19% of the samples were in the category of 10,000/ml or above. L. pneumophila, when present in dental-unit water, never reached concentrations of 1,000/ml or more. Microscopic examination with fluorescent-antibody staining indicated that the contamination was in the dental-unit water lines rather than in the handpieces. Legionella spp. were present in 61% of potable water samples collected for comparative analysis from domestic and institutional faucets and drinking fountains; this percentage was not significantly different from the rate of detection of Legionella spp. in dental-unit water. However, in only 4% of the potable water samples did Legionella spp. reach concentrations of 1,000 organisms per ml, and none was in the 10,000 organisms-per-ml category, and so health-threatening levels of Legionella spp. in potable water were significantly lower than in dental-unit water. L. pneumophila was found in 2% of the potable water samples, but only at the lowest detectable level. The results demonstrate that high concentrations of Legionella spp. frequently develop in dental-unit water lines. They suggest that, although L. pneumophila is not the dominant component in dental-unit water, heavy exposure to species of Legionella should be investigated as a potential health risk for dental personnel and their immunocompromised patients.

Update on infectious risks associated with dental unit waterlines

“…Human pathogenic microorganisms such as Legionella pneumophila, Mycobacterium sp. and Staphylococcus aureus (Table 1) have already been isolated from DUWLs (Atlas et al, 1995;Porteus et al, 2004;Singh & Coogan, 2005;Szymań ska, 2005;Tambekar et al, 2007;Barben et al, 2009;Dahlen et al, 2009). Pseudomonas aeruginosa has been isolated in 15-30% of DUWLs (Barbeau et al, 1996;Monarca et al, 2002).…”

“…Finally, a single case of fatal pneumonia due to Legionella dumoffi was reported in a Californian dentist daily exposed to the contaminated water of his DUWL. However, the evidence linking the disease to DUWLs was only circumstantial (Atlas et al, 1995). Infectious risks associated with dental unit waterlines…”

Bacterial and viral pathogens in saliva: disease relationship and infectious risk

“…Legionellae have been isolated from sputum and other body fluids and sites (123). L. pneumophila has also been recovered from dental unit water in England, Germany and Austria (184), and from 8% of dental units in the USA (18). However, no evidence exists to incriminate dental units as a significant source of legionellosis.…”

Aerosolization of mycobacteria and legionellae during dental treatment: low exposure despite dental unit contamination

“…Legionella spp. have been reported in 50-68% of dental units (Luck et al, 1992;Atlas et al, 1995;Zanetti et al, 2000), at times reaching levels as high as 1 E + 02 to 1 E + 05 colony-forming units (cfu) per millilitre (Barbeau et al, 1998). The primary route of Legionella spp.…”