THE EFFICACY OF CHLORINATION AND FILTRATION IN THE CONTROL AND ERADICATION OF LEGIONELLA FROM DENTAL CHAIR WATER-SYSTEMS

The apparent failure of hyperchlorination and continuous dosing with chlorine to eliminate Legionellae from a dental teaching hospital water supply prompted a prospective study to evaluate charcoal filters as a means of decontamination. Legionella pneumophila serogroup 10 and L. bozemanii serogroup 2 were isolated from dental units yielding 101-103 colony forming units (cfu) ml-1 with total bacterial counts in the range 102-> 104 cfu ml-1. After chair-side installation of charcoal filters bacterial contamination of the dental unit water was prevented and Legionellae were initially not detected, but after 7 days the total count returned to pre-filtration levels of >104 cfu ml-1; L. pneumophila serogroup 10 was eliminated but L. bozemanii serogroup 2 persisted. These results suggest that neither chlorination nor charcoal filtration deal adequately with the potential hazard of Legionella spp. in dental water. © 1990.