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Can the risk of SARS-CoV-2 infection be reduced by disinfecting surfaces?

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While scientists work to identify therapeutics and vaccines to protect us against SARS-CoV-2, the most effective method of controlling the spread of the virus is through good hygiene and decontamination practises. Coronaviruses are made up of RNA and proteins that are surrounded by a protective fatty layer that is easily pulled apart by soaps and alcohols. Bleach is also effective at destroying SARS-CoV-2, but how the molecules in bleach act on the virus remains largely unknown.

Why does soap work well against SARS-CoV-2?

SARS-CoV-2 virus particles are made up of the virus’s genetic information, encoded in RNA, and a set of proteins that are key for: initiating infections, making new virus particles, and releasing new virus particles from infected cells for onward spread. The viral proteins are held in a specific three-dimensional structure by interactions and chemical bonds between the molecular building blocks (called amino acids) that make up the protein. The viral RNA and proteins are surrounded by a lipid (fatty) membrane, known as the envelope, to form the viral particle. The bonds holding the viral RNA, proteins and outer membrane together are weaker and the virus relies on the lipid membrane for its shape, integrity and for infecting cells.

Soap dissolves fat; therefore, it breaks open the lipid membrane so that the virus particle collapses and is no longer infectious. In addition, soap and detergents are ‘surfactants’, compounds that are made up of a head that is attracted to water (hydrophilic) and a tail that is attracted to fat and grease (hydrophobic).[1] Therefore, when amphipathic (having both hydrophilic and hydrophobic parts) soap molecules encounter the lipid membrane of a virus, the hydrophobic tail sticks to the fatty membrane while the hydrophilic head is attracted to water, so that the virus is lifted off and washed away. As the virus becomes dislodged, it is surrounded by more soap molecules, which break open the lipid viral membrane and destroy the virus.

Our skin has hydrophobic properties similar to those of the lipid membrane of the virus. Consequently, the virus sticks to our skin better than household surfaces, so that when we touch a contaminated surface the virus lifts off and sticks to our hands instead. Warm water does not contain surfactants and, when used alone, it is less effective at lifting the virus off household surfaces or our hands compared to soapy water. The effectiveness of various household agents has been studied for other viruses with lipid envelopes like SARS-CoV-2; it was shown that water alone could not inactivate the virus unless the water temperature was raised to over 56 °C.[2][3]

What are the effects of alcohol-based antiseptics against SARS-CoV-2?

Most alcohol-based antiseptics contain either ethanol, isopropanol, or a combination of these molecules dissolved in water. Alcohol-based products inactivate SARS-CoV-2 virus particles by disrupting the structure of the proteins (a process called denaturing) on the surface of the virus. When alcohols are applied to the virus, they displace the hydrogen bonds between amino acids that hold the viral proteins in shape, causing the proteins to lose their structure and function, thereby inactivating the virus. The water in the antiseptic also plays a key role as proteins are difficult to disrupt by this method in the absence of water. This means that alcohol solutions are most effective when they contain 60–80% alcohol rather than 100%.

Alcohols also disrupt the virus lipid membrane, but this occurs by a different mechanism. The higher the lipid content and the larger the virus particle, the more susceptible the virus is to alcohols.[4] The alcohols used in antiseptics are small polar molecules that can interact with the surface of the lipid membrane. When alcohols are present in sufficient concentrations, they disrupt the ordered structure of the membrane, breaking open the virus.

In a recent study, the antiviral actions of WHO-recommended formulations of alcohol-based hand rub and commercially available alcohols (ethanol and isopropanol) were tested on SARS-CoV-2.[5] The study concluded that both WHO formulations as well as the two alcohols were effective at inactivating the virus after 30 seconds.

Can household bleach destroy the new coronavirus?

According to news reports from Shanghai and Gwangju, South Korea, the disinfectant sprayed in the streets is a diluted solution of sodium hypochlorite, or household bleach. Household bleach is commonly used for decontamination purposes as it is relatively inexpensive and works quickly to destroy viruses and other microorganisms. Although the precise methods by which bleach inactivates viruses remain unknown, it is believed that free chlorine destroys proteins and can damage RNA.[6] Prolonged use of bleach is discouraged as it can corrode metal surfaces and lead to respiratory problems over time. Bleach can quickly lose its antiviral activity, as free chlorine levels rapidly decrease following contact with dirt, contaminants, and ultraviolet (UV) light. Therefore, while bleach is an effective decontaminant in many circumstances, its ability to work effectively in dirty outdoor spaces may be compromised.

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References

  1. De Benedictis P, Beato MS, Capua I. Inactivation of avian influenza viruses by chemical agents and physical conditions: a review. Zoonoses and Public Health. 2007;54(2):51-68. DOI: 10.1111/j.1863-2378.2007.01029.x.

  2. Rabenau HF, Cinatl J, Morgenstern B, et al. Stability and inactivation of SARS coronavirus. Medical Microbiology and Immunology. 2005 Jan;194(1-2):1-6. DOI: 10.1007/s00430-004-0219-0.

  3. Greatorex JS, Page RF, Curran MD, et al. Effectiveness of common household cleaning agents in reducing the viability of human influenza A/H1N1. Plos One. 2010;5(2):e8987. DOI: 10.1371/journal.pone.0008987.

  4. Moorer WR. Antiviral activity of alcohol for surface disinfection. International Journal of Dental Hygiene. 2003 Aug;1(3):138-142. DOI: 10.1034/j.1601-5037.2003.00032.x.

  5. Kratzel A, Todt D, V'kovski P, et al. Inactivation of Severe Acute Respiratory Syndrome Coronavirus 2 by WHO-Recommended Hand Rub Formulations and Alcohols. Emerging Infectious Diseases. 2020 Apr;26(7) DOI: 10.3201/eid2607.200915.

  6. Centers for Disease Control and Prevention, National Center for Emerging and Zoonotic Infectious Diseases, Division of Healthcare Quality Promotion. Chemical Disinfectants: Chlorine and Chlorine Compounds. CDC. 2016 Sep.

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