**1. Introduction**

Nosocomial infections, also known as Healthcare-Associated Infections (HAIs), are defined as infections which were absent at the time of hospital admission that a patient acquires during their stay in a hospital or other healthcare facilities [1]. Populations that are at risk for HAIs are immunocompromised patients in Intensive Care Units (ICUs), those in burn units, those undergoing organ transplants, or older patients and neonates. Extensive studies have been carried out by the World Health Organization (WHO) showing that the most frequent nosocomial infections globally include catheter-associated urinary tract infections, central-line associated bloodstream infections, ventilator-associated pneumonia, and surgical site infections [1].

It has been estimated that, in Italy, 5–8% of hospitalized patients contract nosocomial infections every year and 450,000–700,000 HAIs occur in hospitalized patients; these data refer to urinary infections, followed by infections of surgical wounds, pneumonia, and sepsis [2,3].

Risk factors that promote nosocomial infections—other than patient susceptibility, such as immunosuppressed patients in ICUs—include poor hygienic conditions such as improper hand hygiene of Healthcare Sta ff (HCS) or contaminated air and water [1]. The water supply system in hospitals may constitute a source of HAIs caused by opportunistic pathogens such as *Pseudomonas aeruginosa* (*P. aeruginosa*), *Legionella* spp., *Acinetobacter* species, and fungi [4,5]. These organisms are transmitted by direct or indirect contact with water or by inhalation of aerosol generated by a water source [6–8]. *Legionella* spp. are ubiquitous aquatic organisms associated with community-acquired pneumoniae as well as hospital-acquired pneumonia. Direct inhalation of aerosols from environmental colonization is typically the source of infection. As *Legionella* infection is not spread between humans, environmental monitoring of potable water, cooling towers, and related sources is crucial to control the incidence of disease. *Legionella* is able to survive for long periods in water and even to replicate in the presence of disinfectants and some conditions (e.g., pipeline materials, stagnation and sludge formation, parasitism of amoebas and protozoic cysts, and so on) [9].

In recent years, the increasing incidence of both nosocomial and community-acquired *Legionella* infections has been a major public health concern: in 2018, 2964 cases were notified to the National Surveillance System in Italy, with an incidence of 48.9 cases per million inhabitants with lethality rate for community and healthcare cases of 10.9% and 51.7%, respectively [10].

The risk of illness increases dramatically if the germ is found in certain wards such as ICUs, hematology-oncology units, cardiology units, hemodialysis units, and pulmonology units due to the critical nature of these wards for their hospitalized patients [11]. Nevertheless, the real risk of other sources of infection remains partially underestimated when making a correct *Legionella* risk assessment plan in water systems, such as suggested by the Italian Guidelines as the correct strategy to minimize the risk of colonization [12].

Di fferent guidelines and studies have suggested that water outlets for handwashing in hospitals are frequently contaminated with *P. aeruginosa* and other Gram-negative bacteria, such as *Legionella*, which have been linked to nosocomial infections [8,13]. In particular, the presence of *Legionella* in outlets poses a risk of infection during handwashing practices due to aerosol generation.

The key factors for prevention of HAIs in the surgical area are associated with hand hygiene, surgeon handwashing characteristics, and appropriately timed glove use. Hand hygiene is an extremely important measure implemented to reduce HAIs; the WHO published guidelines in 2006 and in 2009 for routine and surgical hand hygiene protocols directed to control resident flora as well as transient microflora [14,15]. There are two primary methods for hand hygiene: antimicrobial or non-antimicrobial soap and water scrub, called the "scrub method", and Alcohol-Based Hand Rub, called the "rub method" [16]. Concerning the surgeon handwashing station characteristics, they are generally made entirely of stainless steel with a tank made of a single plate to guarantee the continuity of the surfaces and to avoid all possible areas of bacterial proliferation (e.g., spaces or grooves). The front part is slanted by 30◦ in order to prevent splashing and direct water contact with operators [17].

Moreover, surgical handwashing points are equipped with two main types of faucets: manual faucets, with a long clinical lever that dispenses and mixes water by use of the elbow or foot to avoid direct contact with the hands, or non-touch water taps, provided with photocell-operated water supply as electronically managed by a photocell sensor, some of them provided by Thermostatic Mixer Valves (TMVs) [18].

Non-touch water taps, also called sensor-activated faucets with TMVs, have been gradually introduced into private and public hospital facilities to prevent patients or HCS from risk of acquiring infection or transferring infection during surgical procedures by touching contaminated taps. These taps work only when the hands are put in front of a magnetic/sensor valve which causes water to flow out and, when hands are removed, the water flow to stop. The presence of a TMV permits the flushing of water through a single pipeline at a fixed temperature (generally about 36 ◦C). The mixing is due to the presence of a cartridge which is able to recall cold water, leading to the desired temperature when mixed with hot water. Hospitals and other healthcare facilities where hygienic measures are very important have started to install this type of touch-free tap system to promote lower water consumption, thus saving costs and preventing HCS from potential recontamination upon hand contact with faucet valves [18]. However, there are no current data that support a decrease in HAIs associated with the use of non-touch water taps [19].

Periodic monitoring of the presence of *Legionella* or other waterborne pathogens in all outlets used for hand hygiene—in particular, during the preoperative phases of hand hygiene in surgeons—represents a preventive measure to avoid handwashing contamination before starting surgical procedures and to control the possible exposure of patients and health professionals.

Our research is presented as the result of a *Legionella* environmental monitoring program, conducted from 2013 to 2019 in 11 hospitals located in di fferent regions of Italy. The analysis of data has identified, as critical points, 52 Surgical Handwashing Outlets (SHWOs) provided by sensor-activated faucets with TMVs with high levels of *Legionella* contamination.

The focus of the study is the analysis of microbiological contamination of SHWOs concerning *Legionella* and *P. aeruginosa*, comparing hot- and cold-water samples supplied by a municipal distribution system. The data obtained are also studied in relation to the SHWO temperatures measured as well as compare the SHWOs technologies—sensor-activated faucets with TMVs versus manual clinical valves without TMVs—to understand the key elements of contamination that could develop a reservoir for *Legionella* and could enhance the risk of infection.
