Advisory on Surface Cleaning and Disinfection for COVID-19

Revised on  09 August 2021
First released on 22 May 2020

1. Introduction
COVID-19 can be acquired through contact with surfaces contaminated with SARS-CoV-2, the virus that causes COVID-19. Laboratory tests have demonstrated that SARS-CoV-2 can survive on environmental surfaces for two to three days1-2, and a study conducted by the Environmental Health Institute of the NEA has detected the presence of SARS-CoV-2 RNA on surfaces of a room occupied by a case. These studies highlight the risk of fomitea-mediated transmission. Disinfection of spaces exposed to COVID-19 cases is thus essential, and ensuring environmental hygiene through regular cleaning of places with high footfall will minimise the risk of transmission in the community.

For general disinfection, a wipe-down of surfaces with an effective disinfectant is recommended. There are many modes of applying chemical disinfectant on surfaces, as marketed by many suppliers. Not all are effective as claimed and some precautionary measures may be needed during application. For example, applications of chemical disinfectant by handheld misters and electrostatic sprayers are not adequate on their own, and should only be used to supplement a wipe-down. Efficacy of most surface coatings, sometimes called self-disinfecting coating, are not supported by robust scientific evidence. As for whole-room fumigation, these are effective for specific purposes, such as in hospitals and laboratories. They must only be executed by trained professionals, as the processes are complex and exposure to chemical vapours can cause harm.

As UVC radiation can cause injury to the skin (e.g. sunburn) and eye (e.g. inflammation of the cornea), NEA does not recommend the household use of sterilisers that use UVC radiation for disinfection. This is because some devices marketed for home use lack safety features that protect users from unintended or accidental exposure to UV radiation. For more information, please refer to the following guidelines/advisory on the use of UVC devices:

1.   Safety Guidelines for Use of UVC Devices   
2.   Advisory on the Use of UVC Sterilisers in the Home

When choosing a disinfectant for use against coronaviruses, suppliers and users must understand the efficacy of the active ingredient(s), the effectiveness and limitations of the applications, and the potential hazards that accompany the product or application. To assist owners and operators of non-healthcare premises in carrying out environmental cleaning for areas exposed to confirmed case(s) of COVID-19, NEA has released a set of Guidelines for In-House Cleaning and Disinfection of Areas Exposed to COVID-19 Cases in Non-Healthcare Premises.

[a] Fomites are objects or materials which are capable of transmitting infectious organisms from one individual to another.

2. Chemical Disinfectants
2.1 Active ingredients

NEA has provided a list of active ingredients and household disinfectant and cleaning products for disinfection of the COVID-19 virus. The listed products contain at least an ingredient that has been shown to be effective against coronaviruses. The right concentration of the active ingredient and contact time are critical for the effectiveness of the disinfection process. 

Other chemicals may be effective, but their performances could be affected by the mode of application, environmental conditions and the short shelf-life. Data is thus required to demonstrate effectiveness of the product used in conjunction with its applicator or according to the accompanying protocol. An example of this group of chemicals is hydrogen peroxide which is marketed in different formulations and applications. Though generally known to be effective, its performance in vapour state may be influenced by humidity. Another example is active chlorine generated from different precursors. Though active chlorine is effective against coronaviruses, the effectiveness of the product which generates active chlorine by electrolysis of sodium chloride is limited by its poor stability.  

Products that have been shown to reduce bacteria or other virus count are not necessarily effective against coronaviruses, as bacteria and different viruses differ in their biological and chemical makeup. Further, test data that use adenosine triphosphate (ATP) levels are NOT applicable to viruses, as ATP is present in bacteria and organic material, but NOT viruses. 

Users must also be aware of the hazards of the active ingredients in use. For instance, alcohol-based products such as those containing isopropanol or ethanol are flammable, and should not be used in the presence of open flame. Concentrated solutions of bleach or benzalkonium chloride can cause irritation to the skin and eyes. As such, gloves should be worn when handling them.

The public is therefore advised to read product labels to look for the active ingredients and their concentrations, to understand their hazards and to ensure that they meet NEA’s guidelines for effectiveness against coronaviruses. 

Importers and suppliers of disinfectant products should also obtain data that demonstrate the effectiveness and safety of the products, as well as data that support their claims. Businesses can contact NEA if they would like to include their disinfectant products in our List of Household Disinfectants and Self-Disinfecting Surface Coating Products Against COVID-19.

2.2 Application of chemical disinfectant

NEA has provided guidelines for safe and effective disinfection of premises. 

2.2.1 Wipe-down

A wipe-down of surfaces with an effective chemical disinfectant is recommended. A wipe-down offers two modes of action in reducing biorisks – i) disinfection and ii) removal of the virus and dirt/organic matter that could interfere with disinfection. 

Other modes of application may be considered to supplement wipe-down, but should not completely replace it. Effectiveness of these applications must be validated and hazards associated with these applications must be fully understood and mitigated before implementation.

2.2.2 Whole room fumigation

Decontamination of entire rooms is carried out by introducing chemical mist or vapour and maintaining the desired concentration for a required duration. The room is then aerated to remove any traces of the chemical disinfectant that may remain. Whole room fumigation is typically carried out using hydrogen peroxide or chlorine dioxide in hospitals and laboratory settings.   

Each decontamination cycle takes between 2 – 5 hours. This decontamination process has been shown to be a reliable method against a wide range of pathogens. 

The following points should be noted for whole room fumigation:

a) Proper sealing of the room during decontamination to prevent escape of the chemical vapours
b) Evacuation of all personnel from the room
c) Close monitoring to ensure that operators and bystanders are not exposed to chemical levels above the safety limit

2.2.3 Hand-held misters

Hand-held misters work by spraying a mist of disinfectant liquids onto the intended surface for disinfection. Another variant of such a device is an electrostatic sprayer, which delivers charged droplets that are attracted to surfaces, resulting in a more even layer of disinfectant on the surface. An effective hand-held misting/spraying process should deposit an even layer of disinfectant liquid on the targeted surfaces with the required contact time.

Hand-held misters are not intended to be used as a primary disinfection strategy. They should be used in conjunction with wipe-downs. Some limitations affecting the efficacy of hand-held misters are:

a) Need to ensure that targeted surfaces are fully covered, including obscure but frequently touched surfaces, e.g. side of a door handle facing the door.
b) The surface should not be grossly contaminated. Otherwise, pre-cleaning is required.  
c) Moisture-sensitive areas or equipment, which should not be neglected during the disinfection process.  

The following points should be noted for hand-held misting:

a) Operators are to be properly protected, not just against the potential risks of viral aerosol but also against the chemical used. For example, the limit of exposure to hydrogen peroxide stipulated by the Ministry of Manpower is 1 ppm over 8 hours.
b) No bystanders are exposed to chemicals at levels beyond the safety limit.

2.2.4 Auto-misters in a space

There have been proposals to install auto-misters which release a spray of disinfectant at regular intervals in spaces such as toilets.

NEA has thus far not received any data that suggests the efficacy of auto-misters. Even if the auto-mister system uses disinfectants that are known to be effective against coronaviruses, there is currently no evidence that light misting of an effective disinfectant has any impact on virus viability on surfaces. The factors that could affect the utility of auto-misters are:

a) Amount of disinfectant dispensed
b) Distribution of the disinfectant, particularly if it reaches areas at high risk for contamination, e.g. the whole door knob
c) Contact time before the disinfectant dries out

Before any implementation, a systematic scientific field test is required to determine the effectiveness and safety of the system. The spraying of such disinfectants may also cause skin, eye or respiratory problems for unprotected persons.

2.2.5 Surface coating

Sometimes termed biocide coating, “self-disinfecting” coating, or protective coating, such applications involve coating surfaces with disinfectants, where there have been claims of long lasting virus inactivation effect (90 days or more). 

To date, NEA has received and evaluated scientific data from suppliers of self-disinfecting surface coating products. Although not all products demonstrate robust scientific data that support their efficacy and durability, those that do are now listed in List of Household Disinfectants and Self-Disinfecting Surface Coating Products Against COVID-19, under a category “Self-Disinfecting Surface Coatings”. Due to the lack of international standards and guidelines for testing the virucidal efficacy of self-disinfecting surface coatings on their short-term and long-term virucidal activity, NEA has provided a Technical Guidance on the Testing of Self-Disinfecting Surface Coatings against SARS-CoV-2.

3. Ultraviolet (UV) Irradiation
Ultraviolet Germicidal Irradiation (UVGI) is a disinfection method that uses short wavelength UV (UVC). This method of disinfection has been applied in the disinfection of surfaces and sanitisation of drinking water. 

The efficacy of UVGI against a range of microbes including SARS-CoV-2 has been demonstrated by numerous studies4-6. However, NEA does not recommend the use of UVC sterilisers marketed for home use against SARS-CoV-2 as the efficacy and safety of these devices have not been proven. 

UV decontamination has the advantage of short turn-around time  (less than 30 min) and not leaving any chemical residues. However, the following should be considered before implementation, whether as a fixed installation or as an autonomous or portable system. 

a) The need for line of sight to be effective. High-touch points that are obscure may be missed, e.g. areas of door handles, handle bars, or toilet flushes not facing the UV light will not be disinfected.
b) The effectiveness of UVGI in inactivation of microorganisms depend on the duration of exposure, intensity, distance of surface from source, and wavelength of the UV radiation. There is therefore a need for careful calibration and monitoring.
c) UV-C systems should be designed for the output at the end of effective life when the UV-C intensity levels are 50-85% or more of that measured at initial operation. Depreciation over useful life should be verified by lamp manufacturers’ specification data.7
d) If UV-C systems are intended to be operated intermittently, this must be factored into the initial system design. Cycling UV lamps on and off may negatively affect the lamp/ballast performance, and life.8

The adverse effects of UVC include potential harm to the exposed eyes and skin. Chronic exposure to UV radiation can also accelerate the skin aging process and increase the risk of skin cancer. The space must thus not be occupied during UVGI, and measures must be in place to prevent accidental exposure9 -10.

UV-C systems also should not generate ozone gas in occupied spaces beyond the acceptable limit (0.05 ppm, 8 hr) stipulated by Singapore Standard SS554: Code of Practice for Indoor Air Quality for Air-Conditioned Buildings.

4. Conclusion
The NEA urges premises owners and operators to maintain high standards of sanitation and personal hygiene to minimise the transmission of COVID-19. Together with the implementation of a structured cleaning and disinfection regime, basics like regular handwashing and the provision of hand soaps and sanitisers are also necessary to keep members of the public safe.

Further information on the General Sanitation and Hygiene Advisory for Premises Owners and Operators can be found here.

  1. Chin. A et al. (2020). Stability of SARS-CoV-2 in different environmental conditions. Lancet Microbe; published online Apr 2. DOI: 10.1016/S2666-5247(20)30003-3

  2. van Doremalen N et al. (2020). Aerosol and surface stability of SARSCoV-2 as compared with SARS-CoV-1. N Engl J Med; published online March 17. DOI:10·1056/NEJMc2004973

  3. Luisa A et al. (2020). A continuously active antimicrobial coating effective against Human Coronavirus 229E. MedRxiv; published online May 13. DOI: 10.1101/2020.05.10.20097329

  4. Branche, C.M. (2009) Environmental control for tuberculosis: Basic upper room ultraviolet germicidal irradiation guidelines for healthcare settings. U.S. Department of Health and Human Services, Centre for Disease Control and Prevention, National Institutie for Occupational Safety and Health, NIOSH Publication No. 2009-105.

  5. Lindsley, W.G. et al (2018) Ambulance disinfection using Ultraviolet Germicidal Irradiation (UVGI): Effects of fixture location and surface reactivity. J. Occup. Environ. Hyg. 15, 1-12

  6. Biasin M. et al, UV-C Irradiation is Highly Effectively in Inactivating SARS-CoV-2 Replication, Sci Rep, 11, 6260 (2021).

  7. 2016 ASHRAE Handbook – HVAC Systems and Equipment, Chapter 17: Ultraviolet Lamp Systems, 2016.

  8. 2016 ASHRAE Handbook – HVAC Systems and Equipment, Chapter 62: Ultraviolet Air and Surface Treatment, 2016.

  9. SCHEER (Scientific Committee on Health, Environmental and Emerging Risks), Opinion on biological effects of UV-C radiation relevant to health with particular reference to UV-C lamps, 2 Febuary 2017.

  10. Talbot E.A. et al. 2002. Occupational Risk from Ultraviolet Germicidal Irradiation (UVGI) Lamps. Int. J. Tuberc. Lung. Dis. 6, 738-41