*Article* **Prevention and Control of** *Legionella* **and** *Pseudomonas* **spp. Colonization in Dental Units**

#### **Benedetta Tuvo 1, Michele Totaro 1, Maria Luisa Cristina 2, Anna Maria Spagnolo 2, David Di Cave 3, Sara Profeti 1, Angelo Baggiani 1, Gaetano Privitera 1 and Beatrice Casini 1,\***


Received: 24 February 2020; Accepted: 17 April 2020; Published: 21 April 2020

**Abstract: Introduction:** Dental Unit Waterlines (DUWLs) have shown to be a source of *Legionella* infection. We report the experience of di fferent dental healthcare settings where a risk managemen<sup>t</sup> plan was implemented. **Materials and methods:** In a Hospital Odontostomatology Clinic (HOC) and three Private Dental Clinics (PDCs) housing 13 and six dental units (DUs), respectively, an assessment checklist was applied to evaluate sta ff compliance with guideline recommendations. DUWLs microbial parameters were investigated before and after the application of corrective actions. **Results:** In the HOC a poor adherence to good practices was demonstrated, whereas protocols were carefully applied in PDCs. *L. pneumophila* sg 2–15 was isolated in 31% (4/13) and 33% (2/6) of DUs in HOC and PDCs, respectively, mainly from handpieces (32%, 6/19) with counts >10<sup>2</sup> colony-forming units per milliliter (CFU/L), often associated with *P. aeruginosa* (68%, 13/19). The shock disinfection with 3% v/v hydrogen peroxide (HP) showed a limited e ffect, with a recolonization period of about 4 weeks. *Legionella* was eradicated only after 6% v/v HP shock disinfection and filters-installation, whilst *P. aeruginosa* after the third shock disinfection with a solution of 4% v/v HP and biodegradable surfactants. **Conclusions:** Our data demonstrate the presence and persistence of microbial contamination within the DUWLs, which required strict adherence to control measures and the choice of e ffective disinfectants.

**Keywords:** Dental unit waterlines; *Legionella* spp.; risk management; disinfection
