Public Release: 

Death of woman from Legionnaires' disease traced to infection from contaminated dental surgery equipment

Doctors recommend multiple control measures to protect public health

Lancet

The Case Report in this week's Lancet details the death of an 82-year-old woman in Italy, which was caused by Legionnaires' disease traced to equipment in a dental surgery she attended shortly before her death. The authors of the Case Report--led by Dr Maria Luisa Ricci at the Istituto Superiore di Sanità, Rome, Italy--recommend a number of control measures at dental surgeries to prevent any similar cases.

In February, 2011, the woman was admitted to the intensive care unit (of the "G.B. Morgagni-Pierantoni" Hospital, Department of emergency Anaesthesia and Intensive Care Unit, Forlì, Italy) with fever and respiratory distress. She was conscious and responsive. Chest radiography showed several areas of lung consolidation. She had no underlying disease. Legionnaires' disease was promptly diagnosed by Legionella pneumophila urinary antigen test and oral antibiotics (ciprofloxacin every 12 h) were started immediately. Sadly, the patient developed rapid and irreversible septic shock and died 2 days later. An investigation to find the source of L pneumophila infection was initiated.

During the 2 to 10 day incubation period necessary for incubation of L pneumophila, the woman had been at home most of the time, leaving only to attend 2 appointments with a dentist. Water samples were taken from the tap and the high-speed turbine of the dental unit waterlines, from the dental practice's taps, and from the patient's home (taps and shower) to investigate possible L pneumophila contamination. All samples from her home were negative on culture, but those from the dental practice were positive for L pneumophila. Laboratory experiments demonstrated genomic matching between L pneumophila found in the patient's respiratory secretion and in the dental unit waterline.

L pneumophila is a Gram-negative bacterium ubiquitous in natural water environments and found also in man-made water systems; it can infect people by inhalation or microaspiration of aerosolised water causing a severe pneumonia known as Legionnaires' disease, mainly affecting elderly and immune-compromised patients, or a flu-like disease, known as Pontiac fever.

Sources of infection have been shown to be primarily air-conditioning systems, hot-water systems, spas, and fountains. Significant contamination of dental unit waterlines with Legionella has been widely documented. Studies have also shown a higher prevalence of antibodies to L pneumophila in the blood of dentists and dental practice staff, suggesting a potential health risk for these workers. However, before this case, the authors were aware of no case of Legionnaires' disease that had been associated with this source of infection.

The authors say: "The case here shows that the disease can be acquired from a dental unit waterline during routine dental treatment. Aerosolised water from high-speed turbine instruments was most likely the source of the infection. Legionella contamination in dental unit waterlines must be minimised to prevent exposure of patients and staff to the bacterium. We suggest several control measures: use of anti-stagnation and continuous-circulation water systems; use of sterile water instead of the main water supply in the dental unit waterline; application of discontinuous or continuous disinfecting treatment; daily flushing of all outlets and before each dental treatment; use of filters upstream of the instruments; and annual monitoring of the waterline. Further useful procedures to prevent legionellosis within dental surgeries can be obtained from [already available] dedicated guidelines."

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Dr Maria Luisa Ricci at the Istituto Superiore di Sanità, Rome, Italy. T) 39-0649902856 E) marialuisa.ricci@iss.it

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