By Hridya Susan Varughese,
PhD scholar, Veterinary College, Bengaluru- 560024
Disinfection is the simplest way of preventing infections by eliminating pathogens. The ongoing corona viral pandemic is a steady reminder of its importance. In principle, it has been in practice since centuries with sulphur compounds being used for disinfection fromthe 18th century plague outbreaks. While use of copper, mercury, salts, alkalis, acids and plant extracts were chemical methods, filtration, burning, fumigation and burial were physical methods. Closer to the 19th century, tyndallisation and autoclaving gained momentum focusing on bacterial spores 1 .The existence of micro-organisms explored by Louis Pasteur inspired the likes of Joseph Lister and Paul Erhlich to pave way for antiseptics- phenols, chlorine, hydrogen peroxide, U.V light, formaldehyde soon to be followed by antimicrobials2 .
While disinfection is an inclusive term, it particularly refers to non-living surfaces, antisepsis refers to living tissue and sterilization refers to removal of all life including spores. Static refers to ‘growthinhibition’ while cidal refers to ‘death’ of organisms. Simple cleaning with water physically removes soil or dirt. Washing with soap or detergents is a preliminary measure as they have triclosan, salicylic acid, and carbolic acids etc. as active ingredients. These are comparatively inferior. The use of triclosan has propelled antimicrobial resistance3. Salicylic acid has a broadly non-specific action and carbolic acid has been linked with skin conditions. Floor disinfectants contain phenol, hydro chloric acid, sodium bisulfate as active ingredients while dish or cloth washing detergents contain surfactants rather than specific germicides facilitating ‘cleaning’ rather than ‘disinfection’.
The mechanisms of action of chemical disinfectants are based on lipid membrane lysis (alcohols), inducing free radical injury (chlorine or hydrogen peroxide), genetic mutations (UV), protein denaturation (formaldehyde, per acetic acid, quaternary ammonium compounds-QAC), hydrogen ion imbalance (acids or alkalis), osmolytic action (NaCl), alkylation of nucleic acids (ethylene oxide) etc4. 2.4% glutaraldehyde is an efficient bactericidal, virucidal and sporicidal agent. 0.5% chlorhexidine, chlorine, iodophores, peroxides, phenolic compounds and 0.025% benzalkonium chloride is highly effective against commensal and pathogenic bacteria. Per acetic acid is effective against yeasts. Alcoholic agents are multipurpose with 70% ethanol or isopropanol effective against bacteria, lipophilic and hydrophilic viruses5.
Hospital disinfection measures are quite elaborate. It encompasses multiple components. Three levels of disinfection are described – High, Intermediate and Low. High level disinfection kills all bacteria, viruses and some spores by use of glutaraldehyde, hydrogen peroxide, Ortho-pthalaldehyde, per acetic acid, sodium hypochlorite. Intermediate level disinfection kills mycobacteria and other pathogens. Low level disinfection kills some viruses and bacteria6. Disinfection of medical devices is dependent on infection risk and are categorized into critical, semi-critical, non-critical. Critical devices are in contact with sterile tissue and blood; they must undergo sterilization example needles. Semi-critical devices do not penetrate sterile tissues but contact mucous membranes example laryngoscope; they must undergo high level disinfection. Non critical devices only touch intact skin, example stethoscope and can be cleaned by low level disinfection5.
Hands are an important transport of infections due to their regular contact with surfaces, people, pets and individual themselves. Community hygiene is centered on hand hygiene. An 11 step hand washing rule practiced for 20-30s has been encouraged by the WHO7. Unless hands are soiled, alcohol based cleansers are preferred over soaps or detergents. A study established the effectiveness of hand sanitizers in inactivating the COVID-19 virus as well. The components were 80% ethanol or 75% propanol, 1.45% glycerol and 0.125% hydrogen peroxide as a base8. Efficacy of hand sanitizers on Staphylococcus and Enterobacteraciae has been described in combination with QAC and aldehydes proving hand hygiene is an important tool in disinfection. Spray fogging of chemicals also has been suggested as a disinfection tool. Alcohol based hand rubs for surgical sterilization has proven effective on various counts.
Other community practices involve surface cleaning with phenolic agents, chlorination of utility water, UV exposure, boiling or pasteurization. Despite its versatility, skin or mucous membrane irritation, corrosive nature, flammability, strong odors and even antimicrobial resistance are some of the drawbacks of disinfectants. Use of protective agents like glycerol or combining different agents can be used to overcome them. Pursuing alternative antimicrobial practices could also be a solution. Many traditional Indian practices have been proven to be set in science. Lime or calcium carbonate used as a white washing agent has a lethal effect on resilient bacterial spores. Turmeric, cloves and other spices have proven antiseptic properties. Common salt aids in osmotic killing of microbes and worms. Sun drying kills fungal spores through desiccation. Vinegar can also kill TB organism9.
Epidemics in history have always imparted lessons. Small pox gave us ‘vaccination’, plague cautioned animal harbingers of disease,cholera sensitized water treatment, HIV and Ebola urged antiviral research. Disinfection remains a sure shot prophylactic especially in the absence of vaccines or therapeutics. In the relentless fight against disease, disinfection stands a silent soldier, forgotten once the war (disease outbreaks) is over.
COVID 19 gave us many things, quarantine, nature rejuvenation, a brief stint at vegetarianism, but most importantly it reminded us disinfection. A simple practice, that could save our health and our finances. With surging incidence rates of COVID 19, it looks like sanitizers, masks, gloves and social distancing is here to stay. So let’s welcome them with open mind, hearts and hands.
Hugo, W.B., 1991. A brief history of heat and chemical preservation and disinfection. Journal of Applied Bacteriology, 71(1), pp.9-18.
Giuliano, C.A. and Rybak, M.J., 2015. Efficacy of triclosan as an antimicrobial hand soap and its potential impact on antimicrobial resistance: a focused review. Pharmacotherapy: The Journal Of Human Pharmacology And Drug Therapy, 35(3), pp.328-336.
Kratzel, A., Todt, D., V’kovski, P., Steiner, S., Gultom, M., Thao, T.T.N., Ebert, N., Holwerda, M., Steinmann, J., Niemeyer, D. and Dijkman, R., 2020. Inactivation of Severe Acute Respiratory Syndrome Coronavirus 2 by WHO-Recommended Hand Rub Formulations and Alcohols. Emerging infectious diseases, 26(7).
Cortesia, C., Vilchèze, C., Bernut, A., Contreras, W., Gómez, K., De Waard, J., Jacobs, W.R., Kremer, L. and Takiff, H., 2014. Acetic acid, the active component of vinegar, is an effective tuberculocidal disinfectant. MBio, 5(2), pp.e00013-14.