Maverick Citizen

Covid-19 Expert Advice #2

Practical guidance on disinfecting

Practical guidance on disinfecting
SARS-CoV-2 does not need strong, dangerous chemicals to kill it – simple exposure to soap and water (for 20 seconds) breaks down the virus membrane very effectively, and kills it. (Photo: Joyrene Kramer)

This is the second of a series of Expert Advisories on how to respond to Covid-19 which will be published from time to time by Maverick Citizen.

This series is co-written by some of South Africa’s leading medical scientists and academics, including some members of the Ministerial Advisory Committee (MAC) on Covid-19. Although not written for or on behalf of the MAC, much of whose important advice is being lost in the corridors of government, it is intended to provide practical life-saving advice based on the best emerging knowledge and evidence of Covid-19.

We are learning all the time, so it is highly likely that advice will change as we learn more about the virus, so keep an eye on any new recommendations. However, the basic principles explained in this series will stand and help inform your decisions.

These are some of the common questions we hear:

“How do I make my workplace or school Covid-19 free after someone tests positive?”

“Should I disinfect my groceries?”

“Should my school use disinfection tunnels? What should I disinfect after my child returns from school?”

“Must I wipe my shoes and wash my clothes after going outside?”

“What should I wipe down when I get in a taxi?”

Fear of contracting Covid-19 has been exploited by companies marketing unnecessary and even dangerous disinfection methods for surfaces, buildings and humans. Even government departments and officials have implemented spraying of outdoor spaces such as in taxi ranks and open streets. This display, often involving suited sprayers, has been called “hygiene theatre”, and can be alarming. At best, these systems are unnecessary and expensive; at worst, they are harmful to human health, the ecosystem and environment, and are ineffective in Covid-19 control.

Here, we try to give clear and practical advice, based on the latest evidence, that allows you to be as safe as possible. More detailed references are listed at the end if you need more guidance.

First, some basics:

  • The risk of being infected by the virus from touching surfaces is still not fully understood. Scientists believe it contributes less to your risk than being exposed to other humans in crowded environments. Physical distancing, ventilation, wearing masks, hand-washing, isolating if symptomatic, and being outdoors as much as possible (which is highly effective at diluting the virus) when you interact with others, are where you should focus energy – see here.
  • The virus is very fragile. It does not need strong, dangerous chemicals to kill it – simple exposure to soap and water (for 20 seconds) breaks down the virus membrane very effectively, and kills it. In addition, sunlight and heat can kill this virus – which means if you must socialise, do so outdoors.
  • There is NO role for “fogging”, “disinfection tunnels”, spraying or “deep cleaning” for Covid-19. These are heavyweight options we occasionally use for other bugs (we don’t use tunnels anywhere!), and in very specific situations, but not for this virus.
  • Many people have seen studies showing that the virus can live on surfaces like metal and plastic for a long time. However, these studies used large amounts of virus (the equivalent of someone coughing on a surface repeatedly at close range), and even then, it has not been established that the virus can infect you via this route. However, scientists think it is probably a route of spread by touching your face after touching a surface, and is less than with respiratory transmission.
  • All this being said, it seems sensible to avoid or clean surfaces that may be contaminated (and there are lots of other bugs that can be transmitted this way, so this could have other benefits, and does no harm).
  • For surfaces you should be suspicious of – high-touch ones like door handles, rails, lift buttons, counters, common work tables – wipe away dirt first, then apply a soapy water mix, which “cleans and disinfects”, and allow 20 seconds for the virus to be killed. It is important to wipe away dirt, especially organic matter, as it inactivates soap’s action.
  • Avoid using shared utensils or cutlery, or anything else, without wiping them down with soap and water first. Wipe your cell phone down every so often, and try not to share. Make it easy to throw away used tissues, paper towels and other waste into a bin.

Note that our advice relates to SARS-CoV-2, the virus that causes Covid-19. Other bugs have different approaches when on a surface, and often need more effort.

There is a host of terms in the infection control field, including decontamination, disinfection, detergent, antiseptic, and cleaning, some of which we have listed at the end if you are interested, but they can be confusing, and it’s unnecessary for understanding how to keep yourself safe from SARS-CoV-2.

So, it is not that hard, and being sensible goes a long way: In summary, wipe away dirt before applying with a soapy water mix (“clean and disinfect”), to surfaces you are suspicious of – high-touch ones like door handles, rails, lift buttons, counters, common work tables – and allow 20 seconds for the viral membrane to dissolve. It is important to wipe away dirt, especially organic matter, as it inactivates soap’s action.

Which soap should I use?

Any hand soap and nearly all kitchen detergents will do an effective job. If the soap makes oil dissolve – whether on your hands, on your dishes, on the floor – it will dissolve the oil-based membrane around the virus, if in contact with it for 20 seconds or more. The recommendation for hand-washing and for surfaces is the same – give the soap enough time to work.

While alcohol-based sanitisers (at least 70% alcohol content) are more convenient (because they dry quickly on your hands) they are actually less efficient than soap and water at killing the virus. So don’t waste them on surfaces unless you want rapid drying, and only use them on your hands if you can’t access soap and water, and only if any obvious dirt is removed and your hands are dry. Soap and water, other alcohol-based solutions, and diluted chlorine and hydrogen peroxide-based liquids are effective for wiping down surfaces. Spray onto a cloth first then wipe.

How often should you clean?

Just be sensible – this depends on how busy the area is. Of course, you want to clean things more often if there is a lot of people traffic, someone in the area is coughing and sneezing, or where people are singing, shouting or talking, or in a high-risk area like a health facility. A taxi would benefit from wipe downs of seats and handles between trips (and ensuring everyone’s hands are sanitised), a shopping counter or credit card machine every so often. For anything left unused overnight, cleaning is not necessary at all.

Otherwise, routine daily cleaning can proceed as usual. Remember “cleaning” means using a detergent and water, and mechanical action. Disinfection is killing the microbe, but only works after cleaning has taken place because many disinfectants get inactivated in the presence of organic matter.

How extensively should you clean?

As above, it is unclear whether anything except the most frequently touched areas are risky (and even then, we are not 100% sure, but it seems sensible to be cautious). Simply allowing time and air movement to dry and dilute the virus out will naturally disinfect rooms, so there is no need for “misting” or “fogging” (which often uses dangerous chemicals). Wipe the common surfaces with soap and water, open all windows, and let nature take care of the rest.

There is no reason to “deep clean” or shut down buildings, especially where windows can be opened. If you want to err on the side of caution, wipe down surfaces, open the windows, and leave for two to three hours, although even this is almost certainly unnecessary.

Practically, what should happen at my gym, school, mall or place of employment?

Most important is to open windows and doors, add a fan if you don’t have windows on two sides, avoid crowding, wear masks, encourage sick people not to come to work, and send sick people home immediately – see here for symptoms. Then, encourage hand washing or sanitising (so as to limit contamination of the commonly touched surfaces), supported by having sanitising stations wherever possible. Physical distancing remains important and regularly cleaned perspex screens may be useful at reception counters or between desks.

Next, identify common-touch areas (and consider highlighting them with signs, to prompt people to not use them unnecessarily), and identify them for regular wipe-downs; in very high traffic areas, half-hourly may be needed, but less often is probably fine in most cases. Occasionally, it may be wise to wipe after every use – in the case of gym equipment, for instance.

Once an area is left overnight, it is very unlikely to have sufficient virus on any surface to infect anyone. Ensure that cleaning staff have access to gloves and masks as some disinfectants can be toxic to the skin. Be considerate of waste workers and waste pickers, and secure higher-risk waste, like tissues, in closed bags.

Laundry is a common question.

As above, the amount of virus on clothing is extremely unlikely to be significant, unless the person wearing them has the virus (and even then, it’s unclear this will allow transmission) or someone near you has been singing, talking or coughing for more than a few minutes (which should never happen, if you do effective physical distancing). Even if contaminated, leaving laundry overnight, or washing (the dilution, detergent and heat of laundering will take care of the virus; cold-water laundering less so, but still very effective with soap) will solve this, but is an overreaction and unnecessary. The likelihood of Covid-19 being spread on shoes, as with laundry, is very low; if you have crawling kids, maybe put them somewhere safe.

Masks need a special mention.

They are warm and moist all day, and you may unknowingly have the virus and be coating it all day long. This may be the one place to err on the side of caution, and launder daily. Always wash your hands after handling your mask and try keeping it on one particular spot (again minimising any potential risk of transmission to surfaces if you are shedding Covid-19 virus). Like with other clothes, have several, so some are being washed, or kept in convenient places.

The cause of risk in public toilets is probably poor ventilation more than contaminated surfaces, so again, opening windows is probably the most important. Encouraging soap and water within public toilets is relatively easy, and closing the lid before flushing (to avoid generating an aerosol; there is some concern that faeces may be infectious), may reduce the need for wiping down surrounding surfaces.

Again: no fogging, misting or deep cleaning is required. The chemicals usually used with these cause skin and lung reactions, and are no more effective than soap and water for this virus.

Gloves are unnecessary for prevention of transmission, also need regular washing as per your hands, and may give you false reassurance  – rather focus on getting soap and water on your hands regularly.

Fancy equipment, like UV lights, can be expensive and can harm your eyes; they may have a role in health facilities in special situations, but really have no role outside of these. Remember that sunlight is an excellent source of free UV light.

“How do I make my workplace Covid-19 free?”

Get the basics right – physical distancing, open windows and doors, masks, hand-washing are most important. Wipe common-use surfaces regularly. Encourage ill employees with Covid-19 symptoms to immediately go home and isolate – see here.

“Should I disinfect my groceries?”

The amount of virus, even if contaminated, is unlikely to pose any threat. If you’re worried, sanitise your hands before and after handling the groceries, rather than wiping down each item. Leaving groceries overnight will likely disinfect them automatically anyway.

“Should my school use disinfection tunnels? What should I disinfect after my child returns from school?”

Disinfection tunnels may harm your child (or you for that matter), and should not be installed anywhere. For school bags, laundry and textbooks – see above, but again very unlikely to be a source of infection. Rather focus energy on educating the child regarding the basics about viral transmission.

“Must I wipe my shoes and wash my clothes after going outside?”

Unless someone was coughing on you, or singing or talking for prolonged periods, no. And you probably have a far, far greater risk of having breathed in droplets at the time, rather than getting it later from your clothes.

“What should I wipe down when I get in a taxi?”

Masks and open windows, and trying your best to distance yourself are your primary defence here. Sanitise your hands on getting in or out, and try not to touch common surfaces.


A few essential definitions are shown below to clarify concepts and misuse of frequently used words, sometimes interchangeably, without a clear understanding of the meaning.

Antiseptic: a substance that prevents or stops the growth or action of microorganisms by inhibiting their activity or by destroying them. The term is used especially for preparations applied topically to living tissue such as 70% propyl, isopropyl and ethyl alcohol (ethanol) with 2% emollient, povidone iodine (no longer recommended) and chlorhexidine 2-4%.

Cleaning: the physical or mechanical removal of foreign material (e.g., dust, soil) and organic material (e.g., blood, secretions, excretions, microorganisms). Cleaning physically, generally removes rather than kills microorganisms. It is accomplished with water, detergents and mechanical action.

Contact time: the time that a disinfectant must be in contact with a surface or device to ensure that appropriate disinfection has occurred. For most disinfectants, the surface should remain wet for the required contact time. For SARS-CoV-2, it takes 20 seconds to dissolve the membrane.

Contamination: the presence of any potentially infectious agent on items such as environmental surfaces, clothing, bedding, surgical instruments or dressings, or other inanimate articles or substances including water, medications and food.

Detergent: a synthetic cleansing agent that can emulsify and suspend oil. Contains surfactant or a mixture of surfactants with cleaning properties in dilute solutions to lower surface tension and aid in the removal of organic soil and oils, fats and greases. Effective against coronaviruses.

Decontamination: a process for rendering medical or other devices safe for reuse on the same or another patient. It includes thorough cleaning, and disinfection or sterilisation depending on the device’s heat tolerance. Disinfection is a part of decontamination and these two terms should not be used interchangeably.

Disinfection: a thermal or chemical process for inactivating microorganisms on inanimate objects.

High-level disinfection: kills all microorganisms, with the exception of small numbers of bacterial spores. Used for endoscopes and heat-labile equipment.

Mid-level disinfection (also intermediate-level disinfection): kills inactivated vegetative bacteria, including mycobacteria, most viruses, and most fungi, but might not kill bacterial spores. Used for large areas of contamination such as blood spills.

Low-level disinfection: inactivates most vegetative bacteria, some fungi, and some viruses including enveloped viruses, in a practical contact time, but does not kill more hardy viruses (e.g. non-enveloped), bacterial genus (e.g. mycobacteria), or bacterial spores. Used for surface disinfection after cleaning. Effective against coronaviruses.

Disinfectants: Chemical compounds that inactivate (i.e. kill) pathogens and other microbes and fall into one of three categories based on chemical formulation: low-level, mid-level and high-level. Disinfectants are applied only to inanimate objects. All organic material and soil must be removed by a cleaning product before application of disinfectants. Some products combine a cleaner with a disinfectant.

Fogging: (fumigation, misting) Dispersing a liquid chemical disinfectant to disinfect environmental surfaces in an enclosed space. Fogging is sometimes indicated after an infectious patient with a highly resistant pathogen (e.g. C difficile), has been discharged and terminal cleaning has been completed. Fogging is to be carried out in a completely empty room with no humans, furniture or obstruction. The room is ready for use after a couple of hours, depending on the contact time. NOT recommended for coronaviruses.

Healthcare areas (also known as patient care areas): patient zones and the surrounding healthcare environment within inpatient (e.g. general wards, specialised wards, patient rooms) and outpatient settings (e.g. examination areas, patient toilets). This area should remain as clean and dry as possible.

Routine cleaning: the regular cleaning (and disinfection, when indicated) of the patient area to remove organic material, minimise microbial contamination and provide a visually clean environment. The frequency of cleaning is determined by indication, but should be at least once a day in the absence of an outbreak.

Terminal (discharge) cleaning: (deep cleaning) cleaning and disinfection after the patient is discharged or transferred, and includes the entire healthcare area. This does not apply to an office area or a gym or school or other work space, where deep cleaning has no place. The removal of organic material and significant reduction and elimination of microbial contamination to ensure that there is no transfer of microorganisms to the next patient. The room can be occupied as soon as terminal cleaning is completed and ready to accept the next patient. DM/MC

Authors: Prof Shaheen Mehtar, University of Stellenbosch; Dr Nomathemba Chandiwana, Prof Francois Venter, Dr Bronwyn Bosch, Celicia Serenata, Dr Esther Bhaskar, Dr Joana Woods all at Ezintsha, University of the Witwatersrand;  Prof Wolfgang Preiser, University of Stellenbosch; Prof Lucy Allais, Department of Philosophy, Wits Centre for Ethics, University of the Witwatersrand; Prof James McIntyre, Anova Health Institute; Professor Shabir Madhi, Respiratory and Meningeal Pathogens Research Unit, University of the Witwatersrand; Dr Aslam Dasu, Progressive Health Forum; Prof Lucille Blumberg, National Institute of Communicable Diseases (NICD); Dr Jeremy Nel, University of the Witwatersrand, Prof Marc Mendelson, University of Cape Town; Dr Elijah Nkosi, Prof Morgan Chetty, both family doctors; Andy Gray, Division of Pharmacology, Discipline of Pharmaceutical Sciences, University of KwaZulu-Natal; Prof Yunus Moosa, University of Kwa-Zulu Natal;  Prof Eric Decloedt, Division of Clinical Pharmacology, Stellenbosch University; Prof Jantjie Taljaard, University of Stellenbosch

References used in this advisory:

  • MMWR/ April 24, 2020/ Vol 69/ No 16. US Department of Health and Human Services/ CDC
  • WHO. Cleaning and disinfection of environmental surfaces in the context of Covid-19 Interim guidance 15 May 2020. WHO/2019-nCoV/Disinfection/2020.1
  • CDC Covid-19. Cleaning and disinfecting your facility.
  • PAHO. The use of tunnels and other technologies for disinfection of humans using chemical aspersion or UV-C light PAHO/CDE/CE/Covid-19/20-0012
  • AFRICA CDC, AND PREVENTION AND THE INFECTION CONTROL AFRICA NETWORK. Position statement. The use of disinfection tunnels and disinfection spraying of humans. May 2020
  • NDOH. Covid-19 disease: Infection Prevention and Control Guidelines, version 2, May 2020
  • Chin, A.W.H., Chu, J.T.S., Perera, M.R.A., Hui, K.P.Y., Yen, H.-L., Chan, M.C.W., et al., 2020. Stability of SARS-CoV-2 in different environmental conditions. The Lancet Microbe S2666524720300033.
  • van Doremalen, N., Bushmaker, T., Morris, D.H., Holbrook, M.G., Gamble, A., Williamson, B.N., et al., 2020. Aerosol and Surface Stability of SARS-CoV-2 as Compared with SARS-CoV-1. N Engl J Med 382, 1564–1567.
  • Chin A et al. Stability of SARS-CoV-2 in different environmental conditions, Lancet Microbe 2020 Published Online April 2, 2020
  • CDC and ICAN. (2019). Best Practices for Environmental Cleaning in Healthcare Facilities in Resource-Limited Settings.
  • WHO (2019) Implementation manual to prevent and control the spread of carbapenem-resistant organisms at the national and health care facility level
  • Guidelines on Core Components in Infection Prevention and Control, WHO, 2016.
  • NDOH. Covid-19 Disease: Infection Prevention and Control Guidelines Version 2 May 2020
  • Goldman E. Exaggerated risk of transmission of Covid-19 by fomites [published correction appears in Lancet Infect Dis. 2020 Jul 30;:]. Lancet Infect Dis. 2020;20(8):892-893. doi:10.1016/S1473-3099(20)30561-2

"Information pertaining to Covid-19, vaccines, how to control the spread of the virus and potential treatments is ever-changing. Under the South African Disaster Management Act Regulation 11(5)(c) it is prohibited to publish information through any medium with the intention to deceive people on government measures to address COVID-19. We are therefore disabling the comment section on this article in order to protect both the commenting member and ourselves from potential liability. Should you have additional information that you think we should know, please email [email protected]"

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