How to disinfect COVID-19?

The COVID-19 pandemic is spreading inexorably across the planet and nearly 3 billion people are confined. The SARS-CoV-2 virus is spreading from person to person via respiratory droplets. We are therefore applying strict barrier measures to limit the number of contaminations, particularly among the elderly, among whom the virus claims the most victims.

As in any outbreak, the physical elimination of the microorganism through disinfection is part of the measures to protect oneself.

What disinfection measures are applicable to COVID-19?

1_ How does the virus spread?

The SARS-CoV-2 virus is transmitted through respiratory droplets emitted when sneezing, coughing or just talking. These droplets, which are larger than 5 µm in size, do not spread more than 1 metre and fall to the nearest surface. When they are smaller, they are in aerosol form but they do not carry a virus: it is said that the virus is not airborne.

When you touch the contaminated surface with your hands and put your hands on your face, the virus can enter the respiratory tract through your mouth, nose or eyes.

To break the pattern of infection it is therefore necessary to: retain the droplets when they are expelled by wearing a surgical mask, wash hands, disinfect contaminated surfaces, prevent the droplets projected directly to the respiratory tract by wearing a mask of the FFP2 type.

Infected respiratory apparatus    –>     droplets      –>    Surface      –>      Hands     –>    mouth, noze, eyes      –>      Healthy Respiratory System     –>     Infected respiratory apparatus  

2_ What are the measures to prevent the propagation of the virus?

We’ve already talked about wearing masks in this blog.

Hand washing should be done very thoroughly with soap as it is a very effective way to remove bacteria and other pathogenic viruses from the skin surface. The washing should last at least 20 seconds, but if you are serious about it, it can take up to 2 minutes. If there is no water available (in public transport, at the office…) or only for a short time (caregiver moving from one room to another) we will use hydro-alcoholic gel, a mixture of ethanol with a final concentration of at least 60%, hydrogen peroxide or chlorhexidine, glycerine and water. Using the appropriate protocol, contact will occur for approximately 30 seconds. The mixture of ethanol and an other disinfectant such as hydrogen peroxide and/or chlorhexidine gives a broader spectrum of action to this product. There are many tutorials on the internet to learn how to wash your hands.

Surface disinfection

Disinfecting surfaces also very effectively prevents the transmission of the virus. We will focus on this particular aspect.

3_ A few definitions

• Antiseptics, disinfectants, biocides

Disinfection is the action of mechanically, physically or chemically destroying microbes on an inert, non-living medium: floors, surfaces, instruments… The aim is to reduce the quantity of microorganisms to a level such that the few remaining elements are not capable of giving an infection. When we destroy all the germs, we then talk about sterilization, but this is not applicable in our case, since we only want to cut the chain of contamination.

A distinction is made between disinfectants for inert surfaces and antiseptics which are products used on the skin. Antiseptics and disinfectants, combined (with other substances) under the term biocides, are able to inhibit the growth of microorganisms (bacteriostasis, fungistasis, virustasis), or have a lethal action (bactericidy, fungicidy, virucidy, sporicidy) by acting simultaneously on several bacterial or viral targets. The action spectra are different depending on the molecule.

From Antiseptiques et désinfectants Dr May Fakhouri

• Targets of antiseptics on bacterial structures

• Targets of antiseptics on viral structures

A distinction must be made between two kinds of viruses: enveloped viruses which are surrounded by a lipid layer belonging to the membrane of their host cell and which they have taken with them, and naked viruses without external lipids. Enveloped viruses are fragile and are transmitted by close contact with biological fluids (this is the case of coronaviruses). Much more resistant naked viruses can survive in the external environment (e.g. polio virus). The Covid-19 virus is an enveloped virus and therefore relatively fragile.

The viral targets of biocides are nucleic acids, proteins and lipids.

From « virus, produits antiseptiques et désinfectants), dossier médico-technique, la norme et ses limites, BH Rihn, T Hadou, A Lefaou, INRS, 2001.

A distinction is made between highly reactive chemical compounds with a brutal, rapid and non-specific action such as halogens, oxidants, aldehydes and strong acids and bases, and chemically stable compounds with a more specific action such as alcohols, quaternary ammoniums, chlorhexidine and phenolic derivatives. Some compounds are non-lethal but are growth inhibitors such as metals (copper, zinc, etc.) and dyes such as methylene blue, formerly used to soothe sore throats, eosin and trypan blue, used to coat herpes or chickenpox pimples.

4_ Use of antiseptics and disinfectants

A number of factors influence the action of biocides. Physical factors such as the temperature, against which the action is doubled for a 10°C increase. That is why it is preferable (when possible) to wash your hands with hot water rather than cold water. There are antagonistic chemical factors such as organic substances. For example, bleach cannot be used on a surface soiled with blood, otherwise its action will be inhibited. Cleaning a surface with a detergent before disinfection both removes organic substances and lowers the initial number of germs to be killed.

There are European standards for chemical antiseptics and disinfectants. The basic standards demonstrate the existence of activity under the most favourable conditions for the product. They are common to all fields and all uses. The application standards try to reproduce for each use conditions close to the real conditions of use.

Some examples of standards :

Antibacterial product : norme NF EN 1040, NF EN 1276, NF EN 13 727, NF EN 1500…

Antifungal product : norme NF EN 1275, NF EN 1650, NF EN 13624…

A virucidal product must claim from the standard NF EN 14476.

For antiseptics it is also necessary to ensure that they are neither toxic nor corrosive.

Biocides fall within the scope of the “Biocides Regulation” (BPR, Regulation (EU) No 528/2012) which replaced the “Biocides Directive” (Directive 98/8/EC) which aims to improve the functioning of the biocides market in the EU, while ensuring a high level of protection of human health and the environment.

A good disinfectant must have a spectrum of activity adapted to the objectives set (for the coronavirus, a virucidal action). Its action must be rapid and not inhibited by interfering substances (blood, pus…) have a prolonged effect and not attack the material. Non-toxic for the personnel, it must be easy to use, must not leave an unpleasant smell and must be stable.

The products used for CBRN decontamination and consisting mainly of a mixture of quaternary ammonium and and hydrogen peroxide are largely oversized for disinfection against Covid-19 since they are also intended for chemical decontamination: it may not be useful to use a hammer to kill a fly!

5_ Vectorisation

Vectorization depends on the type of application. For example, liquid forms are used on mops to wash the floor, spray or sprinkle for slightly larger areas. Surface Disinfection by Air” (DSVA), used mainly in hospitals, consists of nebulising a disinfectant product that falls back onto the surfaces: the operation is carried out in the absence of human presence and makes it possible to reach the most inaccessible surfaces. The “foam” form makes it possible to treat vertical walls and highly porous surfaces. As regards domestic use, the wipes impregnated with the products make it possible to have a product ready for use, keeping well in its original packaging and offering a more precise and safe use.

6_ Covid-19 application

The SARS-CoV-2 virus is a fragile enveloped virus that is transmitted only through respiratory droplets. Studies regarding its resistance in the outdoor environment are inconclusive, but it is thought to survive for approximately 3 hours on outdoor surfaces. However, like all microorganisms, it can resist longer when protected indoors from organic products such as respiratory secretions (up to more than 5 days?).

Which surfaces and how to disinfect them?

It is therefore the surfaces most affected by the hands that transmit the virus. In the outside environment, it is door handles, subway grab bars, elevator buttons. At home, switches, doorknobs, door handles, faucets and other telephones are the main supports. Clothes, for example, can be washed at 60°C for 30 minutes. Surfaces can be disinfected with 0.5% bleach (1 part commercial bleach at 2.6% in 4 parts water or 1 part bleach at 3.6% in 6 parts water) after cleaning with soapy water or a cleaning spray if necessary. An alcohol spray or any other product stamped EN 14 476 will also do the job provided that the instructions on the bottles are followed.

Special case of delicate surfaces and materials

Mobile phones, tablets and other mice are sensitive devices. They are usually not waterproof and should not be soaked in a solution, otherwise the electronic components will be permanently lost. The only effective products are those based on 70° or 60° alcohol (90° alcohol is much less effective because alcohol needs a certain amount of water to act). The alcohol impregnates a microfibre wipe that is rubbed all over the phone, not forgetting the casing. You can use a disinfectant wipe to clean your mouse or computer keyboard.

Should streets and street furniture be disinfected?

More and more cities are cleaning sidewalks and street furniture, usually with 0.5% bleach solutions.

It should be noted that at present there are no studies to say if it is effective. What we do know is that the environmental impact of the disinfectant is certainly not negligible.

Conclusion

Surface disinfection and hand washing are essential to prevent the propagation of Covid-19.

For the hands, Marseille soap or possibly alcoholic gel are particularly indicated: the elimination of the virus from the skin surface prevents contamination of the face and therefore the respiratory tract.

For surfaces, virucidal disinfectants stamped NF EN 14476 should be used. For non-sensitive surfaces, the simplest product is 0.5% bleach. For sensitive products such as computers or mobile phones, 70° alcohol deposited on a microfibre wipe is the right solution.