The Efficacy of Chlorination and Filtration in the Control and Eradication of Legionella From Dental Chair Water Systems

J Hosp Infect. 1990 Jul;16(1):9-18. doi: 10.1016/0195-6701(90)90044-o.


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 10(1)-10(3) colony forming units (cfu) ml-1 with total bacterial counts in the range 10(2)-greater than 10(4) 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 greater than 10(4) 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.

MeSH terms

  • Charcoal
  • Chlorine*
  • Dental Equipment*
  • Disinfection / methods*
  • Filtration
  • Legionella / drug effects
  • Legionella / isolation & purification*
  • Prospective Studies
  • Sterilization / methods*
  • Water Supply*


  • Charcoal
  • Chlorine