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Legionella Pneumonia and Dental Unit Waterlines

Legionella species can cause pneumonia (Legionnaires’ disease) and Pontiac fever, a flu-like illness. The species most commonly associated with disease is Legionella pneumophila. There are numerous serogroups; however, most infections in healthcare facilities are caused by L. pneumophila serogroups 1, 4, and 6.1,2

Each year an estimated 8,000-18,000 hospitalized cases of Legionnaires’ disease occur in the US. However, accurate data reflecting the true incidence of disease are not available because of underutilization of diagnostic testing and under-reporting. It is estimated that only 10% are diagnosed.1,2

People most at risk are males, older (usually 50 years of age or older), heavy alcohol users, as well as people who are current or former smokers, or those who have a chronic lung disease (like emphysema). Immune suppressed persons are more likely to become ill.1-4

The natural habitat for Legionella is water.  Water distribution systems provide favorable water temperatures, physical protection within biofilms, and nutrients to promote growth.

Since the late 1970s, numerous hospitals and long-term care facilities have reported outbreaks of healthcare-associated Legionnaires’ disease. Transmission has been consistently linked to the drinking water distribution systems. The incidence of healthcare-associated infection depends on the degree of contamination of the drinking water system with Legionella and the susceptibility of the patient population to infection.2,3 

Aspiration is a major route of transmission, especially in healthcare-associated pneumonia. Intubation, surgery requiring general anesthesia, and nasogastric tubes have been associated with healthcare-associated legionellosis via aspiration.  Person-to-person transmission does not occur. Aerosolization by use of respiratory tract devices (such as humidifiers and nebulizers), aspiration, and instillation directly into the lung during respiratory tract manipulation have all been linked to infection.2,5,6

In February 2011, an 82-year old woman in Italy was admitted to a local hospital’s intensive care unit with a fever and respiratory stress without an underlying disease.7 The woman was quickly diagnosed as having Legionnaires’ disease Treatment (oral ciprofloxacin) was started immediately. However, the patient developed fulminant and irreversible septic shock and died two days after entering the hospital. An investigation of the source of infection followed.

During the usual incubation period (2 to 10 days), the woman had no obvious exposure risks. The only time she left her home was to attend two dental appointments. Water specimens were obtained from the woman’s home taps and shower as well as the dental office’s cold water tap, high speed handpiece service lines and three-way syringes. All home specimens were negative for Legionella, while all the office’s were positive. Office isolates were then compared to those of the patient’s bronchial aspirates. All were L. pneumophilia from the same highly virulent subgroup 1.

After environmental sampling was complete, the office waterlines underwent disinfection with 12% hydrogen peroxide followed by a shock chlorination treatment. This controlled the L. pneumophilia contamination. No other cases of Legionnaires disease or Pontiac fever were noted among the office’s staff or other patients.

L. pneumophilia contamination of dental unit waterlines is well documented.8,9 Also, dental personnel have a higher prevalence of antibodies to L. pneumophilia.10 This suggests an increased occupational risk. However, until the announcement of the Italian case, there had been no reported cases associated with dental unit waterline emissions generated during routine treatment.

Public health officials indicated that aerosolized water from high speed handpiece was the likely source of infection. Eliminating Legionella contamination of dental waterlines would protect both patients and practitioners. A number of control measures have been suggested. These include: 1) continuous circulation waters systems; 2) using sterile water not only for surgical procedures, but also routine dental treatment; 3) flushing lines between patients; 4) continuous or regularly scheduled disinfection schemes; 5) use of waterline filters and 6) regular testing of water quality.7,11,12

*Director/Scientific Affairs & Research, Organization for Safety, Asepsis, and Prevention.

1. Centers for Disease Control and Prevention. Top 10 Things Every Clinician Needs to Know About Legionellosis. Available at: www.cdc.gov/legionella/top10.htm. Accessed: March 2012.
2. Goetz AM, Yu VL.  Chapter 77 – Legionella pneumophila. In: Carrico R. APIC Text Online 2011. Available at:text.apic.org/item-81/chapter-77-legionella-pneumophila. Accessed: March2012.
3. Zuckerman JM. Prevention of health care-acquiredpneumonia and transmission of Mycobacterium tuberculosis in health care settings. Infect Dis Clin North Am 2011;25:117-133.
4. Buchholz U, Stocker P, Brodhun B. Legionnaires disease—reordered. Infect Control Hosp Epidemiol 2010;31:104-105.
5. Muder RR, Yu VL, Woo A. Mode of transmission of Legionella pneumophila: A critical review. Arch Intern Med 1986;146:1607–1612.
6. Hosein IK, Hill DW, Tan TY, et al. Point-of-carecontrols for nosocomial legionellosis combined with chlorine dioxide potable water decontamination: A two-year survey at a Welsh teaching hospital. J Hosp Infect 2005;61:100–106.
7. Ricci ML, Fontana S, Pinci F, et al. Pneumonia associated with a dental unit waterline. Lancet 2012;379:684.
8. Pankhurst CL, Coulter WA. Do contaminated dental unit waterlines pose a risk of infection? J Dent 2007;35:712-720.
9. Singh T, Coogan MM. Isolation of pathogenic Legionella species and legionella-laden amoebae in dental unit waterlines. J Hosp Infect 2005;61:257-262.
10. Szymanska J. Risk of exposure to Legionella in dental practice. Ann Agric Environ Med 2004;11:9–12.
11. Organization for Safety, Asepsis and Prevention. From Policy to Practice: OSAP’s Guide to the Guidelines, 2003, OSAP, Annapolis, MD, pp. 75-82.
12. Centers for Disease Control and Prevention. Guidelines for Infection Control in Dental Health-Care Settings — 2003.MMWR 52 (RR-17):1-68, 2003.


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