The literature concerning the characteristics of these viruses is still scarce, especially if one considers only COVID-19. The aspects related to the persistence of the virus on surfaces not only represent an environmental and public health problem concerning schools, roads, offices. It is a much bigger problem if hospitals, operating theaters, and sanitary waiting rooms are considered, especially in the new and continuously increasing “COVID departments”. Knowing how the virus behaves in contact with surfaces and with different disinfectants could be important for the sanitization of medical environments. In particular, some authors deal with the optimization of infection control in operating rooms. Some devices are used in hospital operating rooms for single use only, but other devices, surfaces, handles and cords could be transmission vehicles [30
]. Ong et al. 2020 [31
] evaluated the presence of coronavirus in a hospital room of COVID-19 patients. Some surfaces, such as the toilet bowl and the sink, were positive. Room air samples and samples collected after cleaning were negative. The time span varied according to the characteristics of the type of surface: the less-porous ones like plastic and steel were the worst because they absorb droplets less easily, preserving the active virus. Additionally, the different environmental conditions could affect the amount of ventilation of the rooms and the humidity [26
]. According to Van Doremalen et al. [26
], aerosol and surface virus transmission is plausible, since it can remain viable and infectious for hours or days. Kampf et al. [27
] showed how human coronaviruses can remain infectious on surfaces for up to 9 days at room temperature. This is an important factor about coronaviruses’ spread. From this, it is easy to see that if someone tends to touch the environment often—especially if not properly disinfected—the possibility of becoming infected increases. Furthermore, the droplets present in the form of an aerosol of an infected patient can not only easily spread, but also easily settle and last for several hours on a surface. Kampf et al. [27
] investigated different biocidal agents on coronaviruses. They demonstrated how ethanol (78%–95%), 2-propanol (70%–100%), the combination of 45% 2-propanol with 30% 1-propanol, glutardialdehyde (0.5%–2.5%), formaldehyde (0.7%–1%) and povidone iodine (0.23%–7.5%) readily inactivated coronavirus infectivity by approximately 4 log10
or more. Sodium hypochlorite required a minimal concentration of at least 0.21% to be effective. Hydrogen peroxide was effective with a concentration of 0.5% and an incubation time of 1 min. An important finding is the ineffectiveness of chlorhexidine. Within 10 min, a concentration of 0.2% revealed no efficacy against coronavirus. It is a result that does not support some guidelines for dentistry [32
]. Kampf et al. [27
] concluded that these viruses can remain on surfaces up to 9 days and that surface disinfection could be performed with 0.1% sodium hypochlorite or 62%–71% ethanol for 1 minute. According to Warnes et al. [26
], coronavirus persists in an infectious state on surfaces for several days. Warnes et al. [26
] demonstrated the survival of coronaviruses on different surfaces for up to 5 days. Concerning the persistence of the virus on different surfaces, and in particular on metals containing copper, these findings are interesting and could lead to the development of new surfaces with viricidal or bactericidal properties. In confined environments, especially if poorly ventilated, viral particles of less than 0.1 µm in size may remain in the environment as a secondary aerosol. Studies on the topic indicate that a sneeze could release up to 2 million droplets into the air, less than a million from a cough and about 3000 from speaking out loud. The droplets eliminated from the airways, if larger than 100 µm, from a height of 2 m settle on flat surfaces in 3–6 s and reach horizontally about 1.5 m away, then evaporate rapidly, dry and become solid material. This material reaches a size of 2–3 µm. Studies on tuberculosis have shown that this material, maintaining its infectious capacity, could be inhaled and, thanks to its size, reach the most peripheral parts of the lungs, becoming a secondary biological aerosol [26
]. There has not been much discussion about the importance of ventilating environments to prevent SARS-CoV-2 infection, and although the viral particles have not been studied sufficiently for their ability to achieve dangerous concentrations from a distance in confined environments, increased ventilation in an environment is believed to reduce the cross-infection of airborne diseases. Therefore, existing recommendations could be amended to include ventilating public spaces, including means of transport, with suitable means. It is essential to focus on preventing infection by using ventilation suitable to reduce the infectious capacity of the coronavirus. It has been widely demonstrated that natural ventilation causes better air exchange compared to mechanical ventilation—up to 69 changes per hour of rooms when the windows are completely open [33
]. Most international guidelines recommend about 12 changes per hour for isolation rooms in case of infections. Medical and dental staff will have to work safely, and this is complicated by the fact that there are still no official guidelines that tell them how to behave.
Disinfecting surfaces is one of the aspects to which to give greater attention, being done with the detergents already in use today, along with the washing of hands and the use of suitable PPE. In regards to PPE, surgical masks must be used by those who could transmit the virus, but those who work in contact with the patient’s aerosol must use FFP2 and FFP3 (Filtering Facepiece Particles) masks. There should only be one patient in waiting rooms. This is also true in clinical areas; in the case of minors who need an escort, the escort must be at a distance from operators, and must wear a surgical mask. At the end of each session, the surfaces will then have to be cleaned, and the air exchanged. The same procedures should be adopted in the waiting room and in other areas where the patient might pass or touch objects. Certainly, some tools, such as quick tests (once validated), can become useful in the hands of the doctor/dentist to understand if the patient, or some member of their team, is potentially infected.