Japanese Society for Infection Prevention and Control-Online Journal

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The Potential Risk of Legionella Infection in a Dental Unit

Kana FUSHIMI¹⁾, Atsuko SAITO¹⁾, Kazuma SARATANI¹⁾²⁾, Ken TSUCHIYA¹⁾³⁾, Kazuko IKEGAYA¹⁾³⁾, Yuri KASEZAWA¹⁾³⁾, Junichi TOKUHAMA¹⁾²⁾, Seiji HARADA¹⁾²⁾, Hiroshi SHIBATA⁴⁾, Kouji TAKAMORI¹⁾⁵⁾ and Masafumi MASUDA¹⁾⁴⁾
¹⁾Infection Control Committee, Shizuoka City Shimizu Hospital, ²⁾Department of Pharmacy, Shizuoka City Shimizu Hospital, ³⁾Department of Clinical Laboratory, Shizuoka City Shimizu Hospital, ⁴⁾Department of Respiratory Medicine, Shizuoka City Shimizu Hospital, ⁵⁾Department of Oral Surgery, Shizuoka City Shimizu Hospital

In Japan, there are no established standards for the quality of water that is supplied from a dental unit, and there have been no published reports about contamination of the dental unit with Legionella bacteria, showing a lack of interest in such contamination by medical personnel. In our hospital, as part of our countermeasures to prevent hospital infection, we have been regularly performing an environmental investigation on Legionella in water supply system of the hospital since 1997, and, in 2014, we added the water supply from the dental units to this environmental investigation. From dental unit No. 2, 60 CFU/mL of Legionella sp. was detected, and more than 1,000 CFU/mL of Legionella sp. was detected in individual sites, such as the gargle water, the low-speed handpiece, and the air water 3-way syringe of the unit. The following countermeasures were taken. We discontinued the warming of the supplied water. Flushing of the circuit was performed, and dilute sodium hypochlorite was discharged. However, the level of Legionella sp. did not fall below measurable detection limits. We were compelled to replace the unit because, due to the structure of the unit, further countermeasures, such as high temperature sterilization and use of high-concentration antiseptic drug, could not be added.
Most cases of Legionella infection in recent years have been reported as single domestic cases without any obvious source of the infection, which suggests that there is the possibility of previously unrecognized sources of infection. An extremely high potential risk of Legionella infection may be provided by the water supply from a dental unit to produce aerosol.
The hope is that there will be cooperation among the manufacturers of dental units, usage administrators, and the government to establish appropriate management standards and methods to prevent contamination, to control contamination caused by water supply from dental units and to prevent Legionella infection.

Key words：Legionella, dental unit, water supply, environmental investigation

e-mail: smz-hp-kansenbousi1＠bz04.plala.or.jp

Received: November 28, 2017
Accepted: March 27, 2018

33 (4)：136─142,2018