Influencing factors for the persistence of SARS-CoV-2 (COVID-19) exposed in environmental matrices and disinfection methods: systematic review

INTRODUCTION

Coronavirus disease 2019 (COVID-19) is a newly discovered infectious disease caused by a new human virus of the coronaviridae family which was firstly identified in Wuhan, the capital of Hubei province, China in December 2019. It was officially named COVID-19 by the World Health Organisation (WHO) on 12^th February 2020 and also named Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2), because of its 88% genetic similarity with SARS-like coronaviruses of bat origin.¹ The first virus was discovered over 100 years ago and found the human infection in the late 1800s. Over 150 species of RNA virus were discovered and Coronavirus is one of them.² Viruses can be dispersed through aerosols from coughing, sneezing and talking, which in turn contaminate the environment. Its single droplet may easily contain an infectious dose.³

Enveloped respiratory viruses, which are though more vulnerable to environmental stress than non-enveloped viruses, have been shown to persist on surfaces for a certain period. Enveloped respiratory viruses may persist on common hard surfaces longer and cause the potential risk of infection to whoever touches those contaminated surfaces.⁴ When the expelled microorganisms persist with adequate doses of viruses for long enough in the environment to contact with other hosts, indirect and widespread contraction of disease occurs. Once the disease is transmitted from indirect contact, it is challenging to trace the disease's origin, especially in case of contamination from pre-symptomatic patients.⁵ While SARS-CoV-2 is assumed as droplet transmission by WHO claimed that viruses may be transmissible through aerosols and may also survive in water apart from contracting via contaminated surfaces.⁶ SARS-CoV-2 can persist for a few hours in the air after the generation of aerosols.⁷ Virus contamination on air exhaust outlets, means, viruses can be travelled by air.⁸ Besides, SARS-CoV-2 RNA is detected in faeces suggesting virus replication and shedding through patients’ GI tract.⁹ With the likelihood of virus survival in faeces and water, attention should be placed on water-related virus exposures as well.¹⁰

Regarding fomites, these include high touch surfaces of porous and non-porous materials in both healthcare and non-healthcare settings. High touch surfaces of fomites are the highest risk of virus transmission through contaminated environments.¹¹ Various studies of SARS-CoV-2 persistence in common public spaces explored the virus survival duration on the surfaces of furniture, household fixed items, electronic objects, and stairway rails, floors, walls, shelves and countertops. According to WHO, SARS-CoV-2 can survive up to several hours on some porous surfaces such as cloths, cardboards and wood while the virus can be persisting up to several days on different porous materials such as the outer layer of a medical mask.¹² SARS-CoV-2 on non-porous surfaces like copper, glass and stainless steel may persist up to many hours whereas the virus can survive on plastic for many days. Foremost, healthcare settings are essentially under concern for contamination with microscopic virus particles exhaled from patients. Emergency departments, intensive care units, wards, primary health clinics, facilities used for isolation of COVID-19 patients, medical gadgets, surgical tools, instruments in operation theatres, rubbish and waste released from healthcare places (masks and gloves, etc.) are very risky of virus contamination and surface persistence unless effective disinfection measures.¹³ The door handle, toilet bowl and sink were found to be the test positive for the virus. Airflows equipment like vents and Personal Protective Equipment (PPE) also resulted in positive virus tests.⁸ Factors influencing the persistence of SARS-CoV-2 (COVID-19) in different environmental metrics/surfaces are vital to acknowledge in consideration of effective disinfection methods for the prevention of the disease. Many international and national guidelines for preventive measures were developed based on the available information for SARS-CoV-2 so far. The review was to explore the persistence of SARS-CoV-2 (COVID-19) exposed in environmental matrices (air, water, faeces)/fomites surfaces (porous and non-porous) with influencing factors for the virus persistence in environments (such temperature, humidity, pH) and different methods of disinfection. The resulting information will support the relevant authorities in modification of COVID-19 preventive measures accordingly.

METHODS

A systematic review methodology following PRISMA guidelines and its checklist was adopted for this study. PICO (population, intervention, comparison, outcomes) guidelines were used to formulate the research question; “What are the influencing factors for the persistence of SARS-CoV-2 (COVID-19) exposed in environmental matrices and disinfection methods?” SARS-CoV-2 (COVID-19) in environments was assumed as a problem desired to examine (P). The exposure of SARS-CoV-2 with influencing factors (Temperature, Humidity, UV radiation and pH) and different disinfection methods was assumed as intervention (I). The different duration of SARS-CoV-2 persistence in different environmental matrices, various impacts of influencing factors on SARS-CoV-2 in environments and different disinfection methods were measured as outcomes (O). These PICO criteria became key terms for the literature search.

Eligibility criteria

When determining the type of studies, all primary studies published full-text in English since the beginning of 2020, which were conducted in both healthcare and non-healthcare settings were counted. Systematic, editorial and narrative reviews, government and organisation guidelines, patents, books and data linked with various commercial disinfection products were excluded. The consideration of healthcare settings included but was not limited to acute-care hospitals, long-term care facilities, nursing homes and skilled nursing facilities, physicians’ offices, urgent-care centres, outpatient clinics, home healthcare (i.e., care provided at home by professional healthcare providers), emergency medical services, mobile healthcare services and medical clinic embedded with a workplace or school. In non-healthcare settings, the review included the community facilities (schools/daycare centres/ community centres/businesses) and common public spaces (plazas/squares/parks/sidewalks/streets). Any findings, even a single report of the aforesaid outcomes, such as various degrees of SARS-CoV-2 persistence in environments, influencing factors’ impacts on the virus persistence in environments and different methods of disinfection were presumed as eligible for inclusion.

Bibliographic search

The prime databases used for searching articles were Google Scholar, HINARI and MEDLINE/PubMed. Other databases such as EBSCOHOST and Cochrane Library were also explored. By using the predefined keywords, pilot screening was performed and keywords were modified accordingly. Besides, the search strategy was tested with Boolean Operators by two independent investigators and compared the total number of eligible papers found. Whenever significant differences in the number of searched papers had occurred, thorough discussions between investigators were performed to optimise the keywords and searching mechanism. The potential title and abstract screening process was initiated after the confirmation of keywords and search strategy. The full-text screening was then proceeded to filter the eligible articles. Additionally, a manual search and screening of the reference lists were elaborated. Moreover, Medical Subject Headings (MeSH) terms and specific symbols such as the asterisk- (*) marks and dollar signs- ($) were combined in the search mechanism to identify truncation or find the related terms to find relevant articles.

Identification and selection of studies

The fundamental steps for studies’ identification and selection were the title and abstract screening, saving and sorting out potential articles in software like EndNote, filtering the duplicated papers, screening for eligibility of studies and compiling a final selection for analysis. The self-developed screening tool was used to check if the titles/abstracts/full-texts met any of the pre-defined eligibility criteria. Once the titles/abstracts/full-texts met the inclusion criteria or remained unclear, papers were saved for the next-step screening process otherwise excluded. PRISMA 2009 flow diagram was utilised for the screening process. The selection and revision process of obtained papers were performed by two independent reviewers under the supervision of the immediate supervisor.

Quality appraisal

Mixed-Method Appraisal Tool (MMAT) (version 2018) was a promising and reliable tool for critically appraising and used to assess the strength of the evidence quality. Based on the number of criteria met for the respective study designs, the tool yielded scores of 20%, 40%, 60%, 80% and 100%. In this systematic review, the quality appraisal scores of the selected studies were counter-checked by both reviewers to enhance the quality assurance.

Data extraction

The resulting records from the screening process were saved in Endnote (X7) for the effective elimination of duplication. Data abstracting from the selected studies were collected in an excel spreadsheet. A data extraction form was preliminarily developed, piloted with at least six eligible studies and updated as a final data-entry template. Moreover, limitations of the study, recommendations and remarks on the study results were also documented in the data extracting excel sheet.

Data synthesis and analysis

After the detailed construe, all selected articles were categorised into four groups such as studies related to environmental persistence, studies related to influencing factors on the persistence of viruses, studies related to disinfection methods, and cross-cutting studies that included more than one variable. After the data extraction and entry into the finalised excel template, the collected key data were arranged, coded and sorted out the same data points. Descriptive analysis was elected and manual synthesis was applied for the narrative presentation.

Ethical approval

The study was approved for ethical clearance by the Institutional Review Board of the University of Bedfordshire, UK.

RESULTS

Summary of selection process

The total number of 6184 titles and abstracts (3130 from reviewer-1 and 3054 from reviewer-2) were found at the first step of the screening process. 51 relevant published papers (30 from reviewer-1 and 25 from reviewer-2) were identified from other data sources as additional. Of these, 2850 studies were found as duplicates and 3001 studies were as irrelevant. After cleaning out duplicate and irrelevant studies, 333 full-text papers were found includable. Among 333 papers, 282 were ineligible for full-text reviewing due to some reasons (see in the Figure 1), and finally, 51 papers remained for this present review. The characteristics of these included studies were presented in the table-2 in terms of frequency and percentage.

Persistence of SARS-CoV-2 in environmental matrices/surfaces

Apropos of environmental matrices, not only on fomite surfaces and air media but also faeces and wastewater become concerned. Table 3 demonstrated the persistent durations of SARS-CoV-2 RNA in different environmental matrices/surfaces.

Influencing factors for SARS-CoV-2 persistence in environments

Temperature and relative humidity (RH)

Effect on half-lives of SARS-CoV-2 varied with different combinations of temperature and RH. Virus half-lives were prolonged for 27 hours at 10 °C with 40% RH and were reduced to one and half hours at 27 °C and 65% RH. The estimated mean half-lives of the virus were 15.33±2.75 hours with 20% RH, 11.52±1.72 hours with 40% RH, 9.15±3.39 hours with 60% RH and 8.33±1.80 hours with 80% RH at 24°C respectively. The mean half-lives of the virus were estimated as 7.33±1.33 hours with 20% RH, 7.52±1.22 hours with 40% RH and 2.26±1.42 hours with 60% RH at 35°C. Also, virus-like particles (VLP) survived better when it was incubated at 22°C than that at 34°C under dry conditions.^14,15 The persistent durations of SARS-CoV-2 (COVID-19) at different temperatures were presented in Table 4.

Sunlight/UV

Virus infectivity was reduced by far-UVC (222 nm) light for 90% in 8 minutes, 95% in 11 minutes, 99% in 16 minutes and 99.99% in 25 minutes with the dose of 1.2 mJ/cm² to 1.7 mJ/cm².¹⁶

pH/acidity

The pH 2.5 with free available chlorine (FAC) was identified as a potent deactivator for SARS-CoV-2 signifying >99.99% reduction of virus infectivity. Technically, the test solution, acidic electrolyzed water (EW), and ratio played a vital role in the inactivation process. By using the acidic EWs (pH-2.5, FAC-74 ppm) with a 1:9 ratio of the virus: acidic EW, virus titer was reduced by ≥4.25 log₁₀ TCID₅₀/mL with ≥99.99% reduction of infectivity after a one-minute reaction. However, neither visible reduction of virus infectivity could be identified on testing with a 1:1 ratio, an equal volume of virus and acidic EW. Moreover, a 17-days old solution of acidic EW (pH-2.5, FAC-109 ppm) yielded inferior action on deactivation of the virus compared to that of fresh acidic EW solution and 31-day stored acidic EW showed no detectable reduction in the virus infectivity.¹⁷

Disinfection methods in healthcare setting

With quaternary ammonium-based detergent for the floor, a sodium hypochlorite for non-floor surfaces in inpatient rooms and hydrogen peroxide for areas outside the patient rooms, surface disinfection was found effective in the reduction of SARS-CoV-2 persistence. As evidence, 36% of positive samples were reduced to 20% after cleaning with the above-mentioned disinfectants. When the disinfecting process was performed more frequently and thoroughly on floors with 2,500 ppm sodium hypochlorite, the persistence of the study virus in surface samples was found significantly reduced by 3.4%.¹⁸ After cleaning with the combined disinfectant and detergent (e.g., Surfanios Premium), the contamination in samples was considerably reduced from 60% to 4.9% for the floors and all the surfaces directly in contact with patients (such as trolleys, skechers, cuffs, door handles etc.) and from 10% to 5.6% for the surfaces not directly in contact with patients (such as stethoscopes).¹⁹ Moreover, Pulsed Xenon Ultraviolet (PX-UV) reduced the infectivity of SARS-CoV-2 to 99.97% at 1 minute, 99.997% at 2 minutes and 99.992% at 5 minutes. Contamination of N95 respirators in inoculation was reduced to 99.998% with 2 minutes of exposure with PX-UV.²⁰

For the effective decontamination of respirators, the recommended dose and time needed to expose to UV light were 5 mj/cm² UV dose for 11 seconds, 300 mj/cm² for 12 minutes, 1 j/cm² for 36 minutes and 3 j/cm² for 1 hour 40 minutes.²¹ For filtering faceplate respirators (FFRs), a dose of 1 mj/cm² of UV-C was a bottom need for disinfecting. Biosafety cabinets (BSC) were used for minimum level UV irradiation to achieve the target dose of decontamination on FFRs. The minimum duration of irradiation for FFRs was identified as 4.3 hours per side, for PPE as 62 minutes per side and for face shields as 15.6 minutes per side (60 mj/cm² of UV radiation).²² Furthermore, decontamination of SARS-CoV-2 on 3M-N95 with UVC in germicidal UVC device was also discussed that total disinfection was attained within 120 seconds. 1 log reduction of viral titer was identified in 2 seconds of UV exposure per side and 2 log in 54 - 120 seconds per side.²³ Regarding decontamination of SARS-CoV-2 in wastewater, preliminary disinfection in septic tanks was performed with free chlorine N6.5 mg/l for 1.5 hours with the dosage of sodium hypochlorite (800 g/m³). However, 12 hours after sodium hypochlorite had been added to septic tanks, the study virus RNA was significantly detectable again due to the decline of free chlorine. When sodium hypochlorite was increased to 6700 g/m³, SARS-CoV-2 became undetectable in wastewater.²⁴

Disinfection methods in non-healthcare/general setting

With the oligomers disinfectants activated by UV light, complete disinfection happened within 10-15 minutes. However, the effectiveness of oligomers became lower in dark places than that occurred under the light.²⁵ SARS-CoV-2 infectivity was reduced to >90% in 10 minutes and >99.99% in 2 hours on the antimicrobial treated surfaces of stainless steel.²⁶ Regarding indoor environments, Far UVC light (222 nm) showed its effectiveness to deactivate the SARS-CoV-2 as 90% in 8 minutes, 95% in 11 minutes, 99% in 16 minutes and 99.9% in 25 minutes.¹⁶ UVB irradiation at 1.6-0.7 W/m² also deactivated the SARS-CoV-2 faster than that at 0.3 W/m². The effective decontamination of the SARS-CoV-2 in wastewater was achieved by the wastewater treatment, particularly including secondary treatment- (Moving Bed Biofilm Reactor (MBBR), Sequencing Batch Reactor (SBF) and Activated Sludge Process (ASP)) and tertiary treatment-(chlorine and UV).²⁷

DISCUSSION

Until the end of the paper screening process i.e., October 2020, by the Author’s knowledge, this systematic review was the only comprehensive review covering the three areas of environmental persistence of SARS-CoV-2 in different matrices, influencing factors of the virus persistence and disinfection methods obtained from the primary studies full-text published from January 2020. As a strength, this review exclusively focused on the SARS-CoV-2 virus and explicitly included both healthcare settings and non-healthcare settings. However, there were some limitations that the review did not include the possible food contamination, the weather/climate effects and fumigation/spraying effects on the virus.

SARS-CoV-2 virus persistence in environmental matrices/surfaces

Based on the findings of the review, the possible persistence of SARS-CoV-2 in environmental matrices was <4 hours on aluminium, 4 hours on copper, 24 hours on cardboard, 44 hours on glass, 48 hours on stainless steel, 72 hours on plastic and 92 hours on polystyrene plastic. These findings had some variations compared with the findings of Kampf, et al.’s review documented the survival of the coronavirus family on aluminium for 2-8 hours, latex rubber for ≤8 hours, glass for 4 days, plastic for 2-6 days, steel/silicon rubber/ceramic/Teflon for 5 days, a disposable gown for 2 days, metal for 5 days, wood for 4 days and paper for 4-5 days.²⁸ In this review, the most contaminated objects with SARS-CoV-2 in inpatient rooms and staff areas were the mobile phones of the patients, buttons of water machines, elevators, beepers, doorknobs and hand sanitiser dispensers, printers, desktops, keyboards and eye protection/face shields/gloves. In non-healthcare areas, the SARS-CoV-2 virus was detected in the air with an approximate half-life of 1.1-1.2 hours and even robust over 12 hours in aerosol form. The common areas with virus aerosol were found not only in the mobilised areas of Covid-19 patients but also in general public areas and general wards of the hospitals. These findings were consistent with the findings of Tang et al.’s review in which the infectivity of SARS-CoV-2 aerosols was identified as extending up to 16 hours. The risk of SARS-CoV-2 aerosol was also classified as high risk (for healthcare settings/ laboratory) and medium to low-medium risk (for public transportation/ naval vessels, public places, restrooms, churches, prisons, schools, nursing homes, and kindergarten areas) in Tang et al.’s review.²⁹ In this review, contaminated wastewater with SARS-CoV-2 could be infectious for 3-7 days. To compare, Rosa et al.’s review stated that the SARS-CoV virus persisted in wastewater for 2 days at 20 °C and ≥14 days at 4°C.³⁰ This review concluded that the duration of SARS-CoV-2 persistence in faeces was 14-50 days and remained positive up to 15-33 days with negative respiratory samples. The review of Gupta et al. mentioned the same outline for the faecal contamination that was positive for 3-30 days from the onset of symptoms and 3-21 days after the negative nasopharyngeal test.³¹

Influencing factors for SARS-CoV-2 persistence in environments

By changing temperature and humidity, SARS-CoV-2 persistence in environments fluctuated. SARS-CoV-2 persistence on non-porous and porous surfaces was recorded as 28 days and 14 days at 20°C and 7 days and 3 days at 30°C respectively. At 40 °C, 99.99% reduction of virus infectivity on all fomite surfaces within an hour. However, the virus could survive up to 21 days on paper notes at 30°C. Kampf. et al.’s review, though, reported approximately 5 days for non-porous surfaces at room temperature or 20°C.²⁸ This systematic review identified additional facts on the impact of temperature on viral load reduction and the effect of relative humidity (RH) on SARS-CoV-2 persistence in environments which was not included in Kampf, et al.²⁸ This particular review identified that virus decaying was noted approximately 5-10 times faster at 27°C than that at 10°C and 2-5 times even faster with 65% RH than that with 40% and 100% RH. Quick virus decaying was recognized with high temperature and RH (35°C with 60% RH). The virus half-life varied with changing temperature and RH such as 15.33±2.75 hours at 24°C with 20%RH and 2.26±1.42 hours at 35°C with 60%RH indicating the virus was mostly stable at ambient indoor temperature with relatively low RH. This review also identified that >3-4 days at 20°C, 30 minutes at 50°C and only over 4 minutes at 70°C were needed for 99% reduction of the SARS-CoV-2 infectivity in wastewater. The results denoted that the higher titer virus stayed more days in wastewater than the low titer at the same temperature. The higher the temperature was, the faster the reduction of the SARS-CoV-2 infectivity occurred in wastewater. This review’s findings on temperature’s impacts on the virus infectivity were consistent with the findings from Rosa, et al. 's review where SARS-CoV could survive ≥14 days at 4°C and 2 days at 20°C. This review also concluded that the virus infectivity was reduced by 99.99% in 25 minutes by far-UVC (222 nm) light with a dose of 1.2 mj/cm² to 1.7 mj/cm².³⁰ This finding was in line with the findings of Riddell et al.’s review described that the virus was susceptible to the UV light around 253.7 nm. This review also identified the critical role of free available chlorine (FAC) concentration in acidic EW activities on the reduction of SARS-CoV-2 infectivity and recorded that acidic EW (pH-2.5), FAC-74 ppm, potently reduced >99.99% of SARS-CoV-2 infectivity with a 1:9 ratio of virus: acidic EW solution.³² In contrast, Cervino et al.’s review recorded that the range of pH (3-10) did not show any significant changes in the stability of SARS-CoV-2.³³

Disinfection methods

Based on the review findings, ammonium-based detergent, sodium hypochlorite, hydrogen peroxide and combined disinfectant and detergent were recommended for effective decontamination on surfaces and floors. Besides, polymers and oligomers were identified as significant disinfectants for SARS-CoV-2. These agents effectively deactivated the virus under UV light within 10-15 minutes. However, the deactivation actions of these agents did not occur in the darkness. Antimicrobial treatment on the stainless steel was noted for the reduction of SARS-CoV-2 infectivity to >99.99 % in 2 hours. The mentioned findings agreed with Kampf et al. in which a range of disinfectants was recorded as effective decontamination for coronavirus by 4 log₁₀ with 78-95% ethanol, 70-100% 2 propanols, combined of 45% 2 propanols with 30% 1 propanol, 0.5-2.5% glutardialdehyde, 0.7-1% formaldehyde, 0.23-7.5% povidone-iodine, at least 0.21% sodium hypochlorite and 0.5% hydrogen peroxide in an exposure time of 15 seconds to 10 minutes approximately.²⁸ In this review, far UVC light (222 nm), UVB irradiation (1.6-0.7 W/m²), and Pulsed Xenon Ultraviolet (PX-UV) (200–320 nm) deactivated SARS-CoV-2 in indoor environments. This review revealed that contaminated N95 respirators were disinfected 99.998% at 2 minutes of exposure with PX-UV in the UVGI box. Notably, UV light had the effective decontamination of respirators, medical equipment and PPE, however, the benefit of utilisation should be outweighed by the harmful effect and cost. Regarding decontamination of SARS-CoV-2 in wastewater, sodium hypochlorite (6700 g/m3) with free chlorine was effective for preliminary disinfection in septic tanks. Compared with Carraturo et al’s review in which sodium hypochlorite with 10 mg/l dosage provided an effective reduction of infectivity to 5 logs in 30 minutes of exposure.³⁴ However, it would be quite concerned to add the recommended dose of sodium hypochlorite per litre of wastewater to maintain decontamination if the wastewater volume was plenteous. Furthermore, MBBR (Moving Bed Biofilm Reactor), SBF (Sequencing Batch Reactor) and ASP (Activated Sludge Process) were recommended as the effective disinfectants in the secondary treatment of wastewater. For the tertiary treatment of wastewater, chlorine and UV were recommended as effective. This systematic review explored the potential spreading sources of COVID-19 in contaminated areas and the influencing factors for the virus in environments since these could be key determinants for the prolongation of the COVID-19 outbreak. Last but not the least, this research revealed effective disinfection methods to break the chain of transmission of SARS-CoV-2 to prevent the COVID-19 surge.

CONCLUSION

Since the COVID-19 pandemic has been pestilential over a considerable duration, global deployment and financial crisis could not be reversed as before. It brought up essentials to allow the nations fully back to work with effective preventive measures. This systematic review documented the key findings that came out through the hard work of the 51 studies across 16 countries. The findings of this systematic review reflected a comprehensive overview of the persistence of SARS-CoV-2 in different environmental matrices under different conditions and the effects of disinfectants and their techniques on the viability of SARS-CoV-2 in both healthcare and non-healthcare settings. Those findings will be important inputs for authorities in the development of mitigation strategies and policies for effective preventive measures for COVID-19. This particular review advocated that the persistence of SARS-CoV-2 in environments should be counted in consideration of disinfection methods and materials. Besides, the infection control team should be informed to develop proper disinfection guidelines/instructions based on the evidence of review. To optimise, the cleaning interval, mechanism and the agents/methods used for decontamination should be regularly monitored with sampling and testing by a defined supervision team. In conclusion, additional research on the possible food contamination, the weather/climate effects and fumigation/spraying effects on the virus should be advanced.

ACKNOWLEDGEMENTS

The authors would like to express sincere thanks to the research supervisor, co-reviewers, course lecturers from both Universities (STIMU and the University of Bedfordshire, UK) and batch-mates for their academic support, kind guidance and encouragement to conduct this dissertation on systematic review.

Funding: No funding sources

Conflict of interest: None declared

Ethical approval: Not required

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