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How Can Dental Offices Prevent Legionnaire’s Disease?

With the concern about COVID-19, my area recently had something else to be worried about—an outbreak of Legionnaire’s disease. When we return to treating patients, what can I do to prevent this?

With the concern about COVID-19, my area recently had something else to be worried about—an outbreak of Legionnaire’s disease. When we return to treating patients, what can I do to prevent this?

Legionnaire’s disease is a respiratory illness associated with the inhalation or aspiration of water sources (aerosols) contaminated with Legionella pneumophila bacteria. There are more than 50 Legionella species with L. pneumophila being the most common. The largest outbreaks of Legionella have been linked to cooling towers, pools, fountains, ice machines, and industrial water systems.1,2 Managing Legionella is challenging as it survives in biofilm. Biofilm forms easily in pipes and narrow tubing, and is found in nature, industry, healthcare settings, and in dental unit waterlines (DUWL). It is critical to maintain safe water for all items connected to air or water lines (handpieces, ultrasonic lines, and air/water syringe lines) as some microorganisms can be harmful or deadly.3 In 2011, an otherwise healthy 82-year-old woman died from septic shock as a result of acquiring L. pneumophila from contaminated DUWL.3

Understanding the type of source water used in your setting is critical. Two types can be used: municipal water or water in a self-contained reservoir bottle (most common in dentistry). It is critical to consult with your dental unit manufacturer to obtain directions on the type of source water that should be used, as well as products and protocols that can be implemented with the unit to ensure safe DUWL.4 Education of staff, scheduled maintenance, and record keeping help ensure DUWL meet Environmental Protection Agency (EPA) safe drinking water standards (< 500 CFU/mL).4–6 Without these measures, biofilm will continue to proliferate and could cause harm. The 2003 Centers for Disease Control and Prevention (CDC) Guidelines for Infection Control in Dental Health-Care Settings states that bacterial counts in DUWL (for nonsurgical procedures) should be “as low as reasonably achievable” and must minimally meet the EPA drinking water standard of < 500 CFU/mL.4


To ensure DUWL meet EPA standards, these recommendations should be followed:4,5

  1. Consultation with dental unit manufacturer for directions on DUWL products and protocols.
  2. Use commercially available devices, products, and procedures, including self-contained water reservoirs with added cleaning agents designed to isolate water from municipal supplies, chemical treatments designed to inactivate biofilms, slow release cartridges designed to prevent biofilm, in-line microfilters, or a combination of these.
  3. Use safe source water (< 500 CFU/mL) including, municipal, distilled, or sterile water (for surgical procedures).
  4. Self-contained water reservoirs must be maintained according to manufacturer instructions or else they rapidly become contaminated. Self-contained water alone will not eradicate biofilm formation, so controlling the quality via devices, products, or procedures is necessary.
  5. Flush all DUWL for 20 seconds to 30 seconds between patients to remove any possible contamination from the previous patient. There is no longer a need to flush DUWL for 1 minute to 2 minutes at the beginning of the day. Evidence suggests firmly adherent biofilms are not dislodged by flushing alone, therefore, flushing for 20 seconds to 30 seconds is adequate to clear stagnant lines. Flushing alone does not qualify as appropriate quality control.


All clinical staff members should be educated about dental unit water quality, biofilm, water treatment, and dental unit maintenance, including monitoring, to determine the safety of outgoing water. Manufacturers should be consulted for proper instructions and recommended monitoring schedules to maintain safe DUWL. This can be achieved with either commercial water testing products/kits used in the office, or with laboratory testing services.4,5 Once DUWL quality is determined, initial, periodic, or continuous chemical “shock” treatments are recommended to reduce or eliminate biofilm.4


If using municipal source water, you must be aware of boil water advisories. City municipalities must comply with EPA standards and is generally safe; however, contamination sometimes occurs for a variety of reasons (failures in water treatment processes, harmful pathogens identified in the water supply, violations of coliform rules, water main breakages, and natural disasters). Boil-water advisories are issued as a public health announcement indicating that tap water is not safe to drink unless it is first boiled.


  1. Do not deliver water from the public water system to the patient through the dental operative unit, ultrasonic scaler, or other dental equipment that uses the public water system, including patient rinsing and handwashing.
  2. For handwashing, use antimicrobial-containing products that do not require water for use (eg, alcohol-based hand rubs). If hands are visibly contaminated, use bottled water and soap for handwashing.

The following apply when the boil-water advisory is cancelled:4

  1. Follow guidance given by the local water utility regarding adequate flushing of waterlines. If no guidance is provided, flush DUWL and faucets for 1 minute to 5 minutes before using for patient care.
  2. Disinfect DUWL as recommended by the dental unit manufacturer.


Using good quality source water that meets EPA standards, education and training of staff, consulting the unit manufacturer’s instructions, and compliance with DUWL protocols are the best ways to prevent contamination or a Legionella outbreak.


  1. Hamilton KA, Prussin AJ, Ahmed W, Haas CN. Outbreaks of Legionnaires’ disease and pontiac fever 2006-2017. Curr Environ Health Rep. 2018;5:263–271.
  2. Fitzhenry R, Weiss D, Cimini D, et al. Legionnaire’s disease outbreaks and cooling towers, New York City, NY, USA. Emerg Infec Dis. 2017;23:1769–1776.
  3. Ricci ML, Fontana S, Pinci F, et al. Pneumonia associated with a dental unit waterline. Lancet. 2012;379:684.
  4. Kohn WG, Collins AS, Cleveland JL, et al. Guidelines for infection control in dental health-care settings–2003. MMWR Recomm Rep. 2003;52(RR-17):1–61.
  5. Mills S, Porteous N, Zawada J. Dental unit water quality: organization for safety, asepsis and prevention white paper and recommendations 2018. J Dent Infect Safety. 2018;1:1–27.
  6. Miller CH, Palenik CJ. Infection Control and Management of Hazardous Materials for the Dental Team. 4th ed. St. Louis: Mosby; Elsevier: 2010.
The Ask the Expert column features answers to your most pressing clinical questions provided by Dimensions of Dental Hygiene’s online panel of key opinion leaders, including: Jacqueline J. Freudenthal, RDH, MHE, on anesthesia; Nancy K. Mann, RDH, MSEd, on cultural competency; Claudia Turcotte, CDA, RDH, MSDH, MSOSH, on ergonomics; Van B. Haywood, DMD, and Erin S. Boyleston, RDH, MS, on esthetic dentistry; Michele Carr, RDH, MA, on ethics and risk management; Erin Relich, RDH, BSDH, MSA ,on fluoride use; Kandis V. Garland, RDH, MS, on infection control; Mary Kaye Scaramucci, RDH, MS, on instrument sharpen­ing; Kathleen O. Hodges, RDH, MS, on instrumentation; Karen Davis, RDH, BSDH, on insurance coding; Cynthia Stegeman, EdD, RDH, RD, LD, CDE, on nutrition; Olga A.C. Ibsen, RDH, MS, on oral pathology; Martha McComas, RDH, MS, patient education; Michael W. Roberts, DDS, MScD, on pediatric dentistry; Timothy J. Hempton, DDS, on periodontal therapy; Ann Eshenaur Spolarich, RDH, PhD, on pharmacology; and Caren M. Barnes, RDH, MS, on polishing. Log on to​​asktheexpert to submit your question.

From Dimensions of Dental Hygiene. April 2020;18(4):60.

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