Environmental Disinfection Strategies to Prevent Indirect Transmission of SARS-CoV2 in Healthcare Settings

(1) Introduction: The novel respiratory syndrome coronavirus 2 (SARS-CoV-2), also called coronavirus disease 2019 (COVID-19), is rapidly spreading in many countries and represents a public health emergency of international concern. The SARS-CoV-2 transmission mainly occurs from person-to-person via respiratory droplets (direct transmission route), leading to the onset of mild or severe symptoms or even causing death. Since COVID-19 is able to survive also on inanimate surfaces for extended periods, constituting an indirect transmission route, healthcare settings contaminated surfaces should be submitted to specific disinfection protocols. Our review aimed to investigate the existing disinfection measures of healthcare settings surfaces, preventing the nosocomial transmission of SARS-CoV-2. (2) Materials and Methods: We conducted electronic research on PubMed, Scopus, Science Direct, and Cochrane Library, and 120 items were screened for eligibility. Only 11 articles were included in the review and selected for data extraction. (3) Results: All the included studies proposed the use of ethanol at different concentrations (70% or 75%) as a biocidal agent against SARS-CoV-2, which has the capacity to reduce the viral activity by 3 log10 or more after 1 min of exposure. Other disinfection protocols involved the use of chlorine-containing disinfectant, 0.1% and 0.5% sodium hypochlorite, quaternary ammonium in combination with 75% ethanol, isopropyl alcohol 70%, glutardialdehyde 2%, ultraviolet light (UV-C) technology, and many others. Two studies suggested to use the Environmental Protection Agency (EPA)-registered disinfectants, while one article chooses to follow the WST-512-2016 Guidance of Environmental and Surfaces Cleaning, Disinfection and Infection Control in Hospitals. (4) Conclusion: Different surface disinfection methods proved to reduce the viral activity of SARS-CoV-2, preventing its indirect nosocomial transmission. However, more specific cleaning measures, ad hoc for the different settings of the healthcare sector, need to be formulated.


Introduction
The new severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was first detected in Wuhan (Hubei province, China) at the end of December 2019, and now, it is rapidly spreading all

Protocol and Registration
The protocol for systematic reviews provided by the PRISMA statement [26] was followed to select methods and inclusion criteria.

Inclusion and Exclusion Criteria
This review included all the studies that investigated possible strategies for the disinfection of healthcare settings surfaces against the spread of SARS-CoV-2. Surfaces taken into consideration were tables, door handles, floors, airflow of both medical personnel and patients' dedicated rooms, instruments, and devices used for patient care. Only articles written in English were selected.

Search, Study Selection, and Data Collection Process
An electronic literature search was conducted using PubMed, Scopus, Science Direct, and Cochrane Library databases with the objective of finding recent research concerning the disinfection measures for nosocomial surfaces contaminated by SARS-CoV-2. Our review included institutionally approved disinfection protocols and self-reported disinfection measures experienced in hospital areas affected by the virus. The keywords used for the research in all the above-mentioned databases were combined with the Boolean term "AND": "SARS-CoV-2", "COVID-19", "contaminated surfaces disinfection", "healthcare settings surfaces", selecting paper abstracts and titles as the search field. The eligible articles for our review were selected by two researchers (G.M. and D.L.), who independently evaluated title, abstract, and full text of the found studies. From each included items, data collection was performed by two reviewers (G.M. and D.L.). The following information was extracted from the studies: healthcare setting area subjected to disinfection, type of biocidal agents used to disinfect nosocomial surfaces from SARS-CoV-2, and when explained, the frequency with which the disinfection protocol should be repeated in order to obtain strict cleaning. Figure 1 shows the flow chart used for this review.

Study Selection and Characteristics
After the research on the four databases (PubMed, Science Direct, Scopus, and Cochrane Library), a total of 151 items were found. After duplication removal, 120 articles were submitted to title, abstract, and full text examination. Since this review included only English publications, 12 studies were not selected, because they were written in Chinese; fifty-five articles were excluded based on title; twenty-five based on abstract, and seventeen after a full-text evaluation. Data extraction was consequently performed for the 11 selected studies. Principal outcome measures reported in this review were: (1) type of biocidal agents used for surfaces/floor disinfection, (2) required contact time and frequency for the disinfectant to act, and (3) the area of the healthcare setting in which the disinfection protocol was implemented.

Study Selection and Characteristics
After the research on the four databases (PubMed, Science Direct, Scopus, and Cochrane Library), a total of 151 items were found. After duplication removal, 120 articles were submitted to title, abstract, and full text examination. Since this review included only English publications, 12 studies were not selected, because they were written in Chinese; fifty-five articles were excluded based on title; twenty-five based on abstract, and seventeen after a full-text evaluation. Data extraction was consequently performed for the 11 selected studies. Principal outcome measures reported in this review were: (1) type of biocidal agents used for surfaces/floor disinfection, (2) required contact time and frequency for the disinfectant to act, and (3) the area of the healthcare setting in which the disinfection protocol was implemented.

Results of Individual Studies
The included studies highlighted that different surface disinfection methods may be performed in order to prevent the indirect nosocomial transmission of SARS-CoV-2 (Table 1) by inactivating its virulence.
Kampf et al. [27] analysed different surfaces of healthcare settings, without specifying the department in which the analysis was conducted. According to this review, a significant inactivation of SARS-CoV (isolate FFM-1 and Hanoi strain) infectivity was reached in suspension tests using the following disinfectant agents: the utilization of 78-95% ethanol guaranteed a viral activity reduction of approximately 4 log 10 or more (with a contact time of 30 s). The same result was obtained with glutardialdehyde 0.5% (contact time of 2 min) and 2.5% (contact time of 5 min) acting against Isolate FFM-1 and Hanoi Strain, respectively, while the 30 s contact of 100% concentration of 2-propanol with contaminated surfaces lead to the viral activity reduction of 3.3 log 10 or more. More than 4.3 log 10 viral activity reduction resulted after the application of 2-propanol 45% combined with 1-propanol 30% for 30 s. Formaldehyde 0.7-1% (contact time of 2 min) and povidone iodine 0.23-1% (contact time of 1 min) provided a viral activity reduction equal to or higher than 3log 10 . Carrier tests, reported in the same study, demonstrated that when 70% ethanol, 0.1% and 0.5% sodium hypochlorite, and 2% glutardialdehyde are allowed to act for 1 min on the contaminated surface, they brought to a viral activity reduction of 3.0 log 10 or more. Coronavirus 2 is a new virus, and for this reason, limited research is available to date: in fact, the authors specified that the data reported in their study referred to severe acute respiratory syndrome coronaviruses for suspension tests and to human coronaviruses in general for carrier tests and that they expect similar effects against the novel SARS-CoV-2.
Dexter et al. [28] shared a surface disinfection protocol to manage the transmission of the pathogen in operating rooms (OR). This protocol requires the use of disinfection wipes (with anti-viral activity) containing a quaternary ammonium compound and alcohol, and for improved routine and terminal cleaning, it foresaw the utilization of a quaternary ammonium compound spray with a top down approach and 1-3 min of contact. This operation should be repeated twice, and at the end, a dry microfiber cloth should be used to wipe the disinfected surfaces. High-risk operating rooms should receive an additional measure, which include the use of ultraviolet light (UV-C) for 20-30 min.
According to Ti et al. [29], the disinfection of floors, surfaces, and computer screens of OR should be performed using Chlor-Clean (floor, surfaces) and Mikrozid (computer screens).
For burn wards disinfection, Li [30] et al. demonstrated that 1000 mg/L chlorine-containing disinfectant or 75% alcohol (with a contact time of 30 min) are effective on table surfaces, using a wipe or soak disinfection method and on the ground, using wipe or soak method (from the outside to indoors).
The environmental protection agency (EPA)-registered disinfectants [34] against human coronaviruses (Table 2) are cited in the study by Chandy et al. [31] and in those by Ather et al. [35], in order to clean all the SARS-CoV-2 contaminated surfaces of the interventional radiology department and dental care unit, respectively, such as hydrogen perioxide, phenolic, quaternary ammonium combined with ethanol or with isopropanol, and sodium hypochlorite.
Huang et al. [32] proposed the application on the surfaces of 1000 mg/L chlorine-containing disinfectants, wiping it twice with 75% ethanol and the use of 1000 mg/L chlorine-containing disinfectants once every 4 h for the ground cleaning.
Finally, the use of isopropyl alcohol 70% with the wipe method is foreseen for the radiology department in the study by Goh et al. [33].
Disinfection protocol for the Oral and Maxillofacial Surgery Unit proposed by Yang et al. [36] referred to the WST-512-206 Guidance of Environmental and Surfaces Cleaning Disinfection and Infection Control in Hospitals [37], which is shown in Table 3. Although the disinfection protocol reported by this study has been conceived for hospital settings, the authors suggested to apply it to dental units and maxillofacial surgery departments, which require the same need for cleaning strategies.
Wei et al. [38] described the environmental disinfection protocol against COVID-19, which is performed in the Radiation Oncology Department in of Hubei Cancer Hospital in Wuhan (China). For clean zones, authors wiped down all surfaces with disposable disinfecting wipes or 75% ethanol. All the surfaces of contaminated zones were disinfected twice daily with disposable disinfecting wipes or 75% ethanol. Ground of all the areas was disinfected twice daily with 1000 mg/L chlorine-containing disinfectants with spray method. At the end of the day, the surfaces were wiped down with 75% ethanol, the large equipment were disinfected with movable UV lights for 1 h and the ground was cleaned with 1000 mg/L chlorine-containing disinfectants.
According to Chen et al. [39], surfaces of the contaminated zone of the radiation oncology department should be cleaned using 2000 mg/L chlorine disinfectant for at least 30 min and 75% ethanol (following the manufacturer instructions).
In conclusion, some of the included studies divided the environment in different at-risk zones, each of which should be cleaned followed specific protocols. For example, Wei et al. [38] and Chen et al. [39] divided the radiation oncology unit in a contaminated, semi-contaminated, and clean zone (Table 1), while Yang et al. [35] divided the Oral and Maxillofacial Surgery Unit in a low-, medium-, and high-risk area ( Table 3). The radiology department and the ward unit in the study by Goh et al. [33] and Li et al. [30], respectively, foresaw the division in a clean and dirty area. According to the Guidelines for Infection Control in Dental Health-Care Settings (2003) [40], clinical contact surfaces and housekeeping surfaces (floors, walls, sinks) should be differentiated, since these latter have a lower risk of disease transmission, and for this reason, they can be disinfected with less meticulous methods.

Discussion
This paper had the objective of reviewing the existing literature, concerning the biocidal agents that are used in order to ensure healthcare settings surfaces disinfection against SARS-CoV-2.
The transmission of severe acute respiratory syndrome coronaviruses occurs not only thorough direct physical contact with infected subjects or large-droplet spread but also via contact with environmental contaminated surfaces (indirect transmission) [41,42]. Viruses are pathogens commonly present in hospitals and many of them, including human coronavirus, can survive for hours on hands but also on environmental surfaces [43,44], creating an outbreak of nosocomial transmission.
The experiment performed by Ashokka et al. [45] in which the production of aerosol was simulated by a three-jet Collision nebulizer and fed into a Goldberg drum, recorded that SARS-CoV-2 would be able to survive for 72 h on plastic and stainless steel, 24 h on cardboard, and 4 h on copper. The virus survived approximately 2.7 h in the simulated aerosol. Similar data were obtained during the same experiment conducted by van Doremalen et al. [21]. Therefore, healthcare settings surfaces decontamination results to be crucial in the prevention of SARS-CoV-2 spread [43].
All the studies proposed alcohol based disinfection agents against SARS-CoV [27,32,33,37,38]. Alcohol-based products inactivate virus particle by disrupting the structure of proteins on the surface of SARS-CoV-2, thorough the mechanism called protein denaturation: alcohol displaces the hydrogen bonds between amino acids holding the viral proteins in shape, and as a consequence, proteins lose their structure and function, thereby inactivating the virus. The research conducted by Hulkower et al. [46] tested the efficacy of 62%, 70%, and 71% ethanol (undiluted), 0.55% orthophthalaldehyde, sodium hypochlorite, and phenol (diluted in hard water) on coronaviruses contaminated healthcare settings hard surfaces, showing that only ethanol has the capacity to reduce the virus infectivity by >3 log 10 after one minute of exposure. Another study [47] proved the efficacy of different biocidal agents against human coronavirus 229E, considering as virucidal effectiveness criterion a reduction of viral activity of ≥3 log 10 : ethanol 70% alone or combined with chlorhexidine gluconate 0.008% and cetrimide 0.08%, phenol 5% plus sodium lauryl sulphate 0.06%, and alkaline glutaraldehyde 2% were able to guarantee an important activity against the virus, as opposed to sodium hypochlorite 0.01%, quaternary ammonium 0.04%, and triple phenolic 0.06%, whose action was not sufficient to inactivate the pathogen.
Several included articles inserted the use of chlorine-containing disinfectants in their cleaning protocols [29,30,32,38]. The exact mechanism by which chlorine kills the viruses is still unclear. The virus inactivation may result from inhibition of protein synthesis, loss of intracellular contents, reduction of nutrients or oxygen uptake, oxidation of amino acids, etc. Agolini et al. [48] reviewed the literature in order to find preventive measures to limit the spread of SARS-CoV. In addition to ethyl alcohol 70%, this review proposed the use of chlorine compounds solutions, after an accurate pre-cleaning, to obtain floor and large-surface decontamination. Phenolic detergent disinfectants could substitute chlorine when corrosion, bleaching, or gas production are to be avoided.
Another effective cleaning method is represented by ultraviolet light (UV-C), which reduces the viral contamination in healthcare settings thanks to its action on surfaces and air column [36]. UV-C (with wavelengths equal to 207-222) is able to damage the proteins on the surface of the virus, preventing them from attaching human cells. UV-C works through the use of lamps producing high-intensity ultraviolet C light, which is an electromagnetic radiation form [49]. The utility of this technology has been proven by Pavia et al. [50], who recorded a viral infection incidence reduction of 44% in a paediatric long-term facility, suggesting that UV-C could be able to eliminate the environment as a source of viral infection. However, according to literature, UV-C disinfection should always be performed in combination with chemical cleaning [51].
The disinfection of air should also be considered, since human coronavirus is able to survive in aerosol for few hours (2.7). Some of the selected items used UV lights twice per day for 1 h each time [37,38] or suggested to guarantee accurate ventilation of the area [38], while others chose to treat positive subjects only in negative-pressure rooms or airborne infection isolation rooms (AIIRs) [34].
One included article [34] explained the cleaning protocol for dental care settings. Dentists are the most exposed workers to the risk of COVID-19 transmission more than general physicians and nurses [52]. For this reason, specific SARS-CoV-2 management protocols are needed not only for hospitals but also for the personal protection and disinfection in dental care units.

Strengths and Limitations of the Study
The restricted number of studies reviewed in this paper may be considered a limitation; furthermore, study designs of the selected items are not uniform and most of them consist of descriptive articles, without any statistical analysis of data. On the other hand, this review succeeded in reporting disinfection protocols for many different hospital areas, giving a complete overview of healthcare settings surfaces management.

Conclusions
The current spread of novel SARS-CoV-2 to many countries requires the development of specific environment disinfection protocols in order to limit its nosocomial transmission. The main biocidal agents proposed by the articles included in this review were alcohol based or chlorine-containing disinfectants, while UV-C technology was suggested to be used only in addition to chemical cleaning. Environmental Protection Agency-registered disinfectants against human coronavirus are also considered effective against the virus. However, more specific disinfection measures, ad hoc for the different settings of healthcare sector, need to be formulated.