Isolation of non-tuberculosis mycobacteria in treated dental unit waterlines

The purpose of the study was to investigate the presence of non-tuberculosis mycobacteria (NTM) in dental unit waterlines that were being routinely treated with an intermittent use waterline cleaner.

The study was conducted at a hospital dentistry clinic where immunocompromised patients are seen. Water samples from two lines on one of two dental units were taken before and after routine weekend chemical treatment. Sampling was repeated on two subsequent occasions, on the same unit, at three monthly intervals. Laboratory techniques included centrifugation and membrane filtration to detect small numbers of organisms.

Mycobacterium simiae was isolated from one of the four pre-treatment samples and from two of the four post-treatment samples. Mycobacterium mucogenicum was isolated from one of the four post-treatment samples.

This pilot study found that NTM were present in DUWLs that were being routinely treated with an intermittent use chemical cleaner. Practitioners are urged to understand the limitations of available DUWL treatments, and to consider the use of sterile water for non-surgical, as well as surgical, treatment of immunocompromised patients.