From Volume 47, Issue 11, December 2020 | Pages 964-967
Antiseptics and disinfectants are an integral part of our life in the ‘new normal’ era. How much do we know of these chemicals, some of which are rather toxic, and may even reduce fertility on prolonged exposure? In this COVID-19 commentary, the authors evaluate the quality of the commonly used disinfectants and antiseptics in dentistry, with particular emphasis on their virucidal activity.
The medical profession was unaware that microbes cause infection until Louis Pasteur proposed the ‘germ theory of infection’ in the 1860s. The concept of surgical asepsis was almost non-existent until then, and this changed in 1867, when Joseph Lister, at the Glasgow Royal Infirmary, Scotland, discovered that carbolic acid spray (phenol) was very effective in preventing wounds from getting gangrenous, and antiseptics could dramatically reduce postpartum maternal mortality after childbirth. Subsequently, disinfectants and antiseptics developed a life of their own, as it were, with the introduction of now famous brands such as Lysol in 1889, and Dettol in 1933. Lysol, in particular, proved its worth during the 1918 influenza pandemic, in which it has been estimated that up to 100 million perished.
Although disinfectants have been used for over a century, their widespread use and utility, both in the clinical as well as domestic and public settings, have been brought into sharp focus by the current coronavirus pandemic (COVID-19) caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It is now known that SARS-CoV-2, as opposed to other coronaviruses, is viciously contagious, and may remain infectious on inanimate surfaces for several days.1 Inevitably then, skin sanitization and surface disinfection have been critical steps in arresting the transmission of the virus at home, in public spaces and in the clinic. This, in turn, has led to a burgeoning industry of disinfectants/sanitizers, and their daily use worldwide. At this juncture, it is worth noting the subtle difference between antisepsis and disinfection. Antisepsis refers to microbial reduction, or kill, on live skin or mucosal surfaces, while disinfection denotes microbial reduction, or kill, on objects, surfaces and in liquids. Thus, all antiseptics are disinfectants, but all disinfectants are not antiseptics.2
The virucidal activity of disinfectants varies depending on the pathogen in question, as well as a number of other factors discussed in detail below. For instance, SARS-CoV-2, a member of the family Coronaviridae, an RNA virus, similar to the severe acute respiratory syndrome (SARS-CoV) and Middle East respiratory syndrome coronaviruses (MERS-CoV), is covered with an outer protein coat easily destroyed by disinfectants, and also readily inactivated by heat as well as ultraviolet (UV) irradiation in comparison to DNA viruses, such as the more resilient hepatitis group of viruses.2,3 Unfortunately, SARS-CoV-2 appears to be far more robust in terms of its infectivity in comparison to their family members, hence the possible reason for its pandemic spread.
The aim of this review is to provide an outline of various disinfectants commonly used in dentistry, their toxicity and their relative virucidal efficacy, particularly with regards to SARS-CoV-2.
In general, it should be noted that all disinfectants are potentially harmful and injurious chemicals, and their improper use leads to unhealthy side effects in exposed clinical staff.4 The fact that dental care workers live, day in and day out, in an ambient environment laced and polluted with disinfectants implies that even small quantities of these noxious chemicals may have an additive and deleterious effect on the general health of exposed individuals over decades of clinical practice. Indeed, some of these chemicals, the quaternary ammonium compounds (the quats), for example, are known to impact sperm quality and reduce fertility (at least in mice). Additionally, their use in poorly ventilated rooms/clinics may result in fire, explosions, gas poisoning or equipment corrosion. Hence, negative pressure clinic ventilation has the dual benefits of containment of microbial spread as well as the dispersal of noxious disinfectant chemicals in the ambient clinic air. The collateral damage, and the insidious environmental pollution of wide, and indiscriminate use of these noxious chemicals, as well as the emergence of multiply drug-resistant bacteria on chronic exposure to disinfectant chemicals leaching into the environment, are worthy of mention in this context.
What follows is a brief narrative on the pros and cons of commonly used disinfectants/antiseptics in dentistry, with particular emphasis on their activity against SARS-CoV-2, together with a tabulated ready reckoner on the utility of agents that are in common use (Table 1). It is worth noting that, due to the short time span since the discovery of SARS-CoV-2, there is no substantive literature on the virucidal efficacy of most of the disinfectants discussed below against the pandemic virus. However, it is the consensus, as SARS-CoV-2 belongs to the Coronaviridae family, and is structurally similar to SARS-CoV and MERS-CoV, the historical data on the virucidal efficacy of the disinfectants on the latter two viruses could be safely extrapolated for the new arrival.
| Chemical/group name | Anti-SARS-CoV-2 activity | Flammability (F) or toxic gas (G) | Hazardous to health | Antiseptic use (on skin) | Use on metallic surfaces | Use on acrylic surfaces |
|---|---|---|---|---|---|---|
| Ethanol | ✓ | F | Low | ✓ | ✓ | X |
| Hydrogen peroxide | ✓ | F | Low | ✓ | ✓ | ✓ |
| Phenols | ✓ | F, G | Medium | X | X | X |
| Glutaraldehyde (and formaldehyde) | ✓ | G | High | X | ✓ | ✓ |
| Sodium hypochlorite | ✓ | G# | High | X | X | X |
| Quaternary ammonium compounds* | Weak/yet unknown | ? | High | ✓ | ✓ | ✓ |
: effective or recommended; X: ineffective or not recommended; G: toxic gas-producing;
: when mixed with ammonia;
: quaternary ammonium compounds, including benzalkonium chloride, benzethonium chloride, alkyl dimethyl benzyl ammonium chlorides (C12–16), alkyl dimethyl benzyl ammonium chloride (C14 60%, C16 30%, C12 5%, C18 5%), alkyl dimethyl ethyl benzyl ammonium chloride (C12–18), didecyldimethylammonium chloride
Alcohols, and alcohol-laced products, are the most popular antiseptics in the current pandemic because they evaporate quickly without soiling/staining surfaces, and are cheap, fast acting, water soluble and universally available. However, the alcohol content of the material should exceed at least 60% for a sanitiser to be virucidal. The Centers for Disease Control (CDC) recommends using either ethyl alcohol- or propyl alcohol-based hand rubs with 60–95% alcohol in healthcare settings.5 Unless hands are visibly soiled, an alcohol-based hand rub is preferred over soap and water due to better compliance compared with the latter combination. Alcohol-based hand rubs are generally less irritant, and are effective in the absence of a sink.
Alcohol combined with disinfectants is also used in dentistry in some jurisdictions for surface disinfection, but authorities in the USA do not recommend alcohol for this purpose as it evaporates relatively quickly with minimal substantivity (ie prolonged persistence). Other disadvantages of alcohol are its limited sporicidal activity and its ready inactivation by organic material. More importantly, alcohol-laced substances are volatile and flammable, and can cause an explosion when used in closed spaces with a high concentration of oxygen.
Glutaraldehyde is perhaps the most popular disinfectant used in dentistry in some countries, while it is banned in others. It is mainly used for so-called cold sterilization or the high-level disinfection of equipment that does not withstand autoclaving procedures (such as fibre-optic instruments).2 All aldehydes are high-potency disinfectants. They are skin irritants and may cause sensitization, leading to both long- and short-term health effects.
Glutaraldehyde is commercially available as a 2% acidic solution, to which an ‘activator’ has to be added to bring the solution to the ‘in-use’ alkaline pH of 8.0. Although the activated solution has a shelf-life of up to 14 days, this should be interpreted with caution as the solution may become prematurely ineffective due to factors such as contamination with organic debris.
Chlorhexidine, a bisguanide disinfectant, is widely used in dentistry as an antiseptic and a plaque-controlling agent. For example, a 0.4% solution in detergent is used as a surgical scrub (Hibiscrub); 0.2% chlorhexidine gluconate in aqueous solution is used as an antiplaque agent (Corsodyl) and a 2.0 % agent as a denture disinfectant. It is a highly cationic bisguanide molecule, usually dispensed as salts of acetate, digluconate, hydrochloride and nitrate. Its substantivity in the oral cavity is mainly due to adsorption on to hydroxyapatite and mucosal surfaces.
Hypochlorites are oxidizing agents and act by releasing halide ions. Although cheap and effective, hypochlorites (eg Chlorox and Domestos) readily corrode metal and are quickly inactivated by organic matter. Chlorine-releasing granules (eg sodium hypochlorite/sodium dichloroisocyanurate) or a liquid solution of hypochlorite at a concentration of 10,000ppm (1%) is used to disinfect surfaces contaminated by blood and body fluid spills. Disposable chlorine-releasing wipes (equivalent to 1000ppm or 0.1% free chlorine) could be employed to clean blood spots from dental chairs (Figure 1).
Povidone iodine (PVP-I) disinfectant, in particular, has better antiviral activity than other antiseptics and has already been proven to be an extremely effective virucidal agent in vitro against SARS-CoV and MERS-CoV. Recent experiments have shown its in vitro activity against SARS-CoV-2 as well.
Phenolic disinfectants are clear, soluble or black/white fluids (black/white fluids are not used in dentistry). They are poorly virucidal and sporicidal. They are particularly useful for gross decontamination of surfaces such as clinic or hospital floors, because they are not easily degraded by organic material. Examples are proprietary preparations of ClearSOL and Stericol. Chloroxylenol (eg Dettol) is also a non-irritant phenolic used universally as an antiseptic; it has poor activity against many bacteria, and its use is limited to domestic disinfection.
Quaternary ammonium compounds, commonly called ‘quats’, are potent disinfectant chemicals very common in household wipes, sprays and other cleaners (Figure 1). They are also used as additives in various soaps and non-alcohol-based hand sanitizers. Quats are members of a large family of compounds and their current worldwide use appears to be second only to alcohols. The US Food and Drug Administration (FDA) has stated that benzalkonium chloride and related quats are useful against SARS-CoV-2, but less so than the alcohols.
The adverse effects of quats include skin irritation on prolonged use, and lung sensitization, aggravating asthma. Additionally, it is known that prolonged exposure to quats may harm sperm quality, reducing fertility and resulting in birth defects, in mice.
Short wavelength ultraviolet irradiation (200–280 nm; UV-C) is known to rapidly disinfect the ambient air, including inactivating any entrained or surface-lying SARS-CoV-2.6 It must be noted that any irradiation shadow areas are not disinfected. Direct UV irradiation of organic glassware, such as polyvinyl chloride or glassware, is not feasible. In terms of its effects on health, there is no evidence to indicate that short exposure to UV light causes either skin genotoxicity or affects the vision. Overnight exposure to appropriate wavelength UV irradiation appears to be a simple, cheap, yet effective engineering control measure for sanitizing exposed surgery surfaces such as clinic floors and cabinet tops.
In conclusion, SARS-CoV-2, being a fragile, protein-coated RNA virus, appears to be susceptible to the vast majority of commonly used disinfectants and antiseptics. In spite of this, its very high transmissibility, infectivity and its prolonged survival in the environment seem to have led to its global spread, causing the current pandemic. Much more research is required to fully evaluate the effectiveness and efficacy of commonly used disinfectants in the battle against this formidable foe.
In general, it is important to choose the least toxic chemical when using a disinfectant because the secondary effects of prolonged exposure to these noxious chemicals may be a health hazard, cause environmental pollution and lead to the emergence of multiply resistant organisms. The bottom line is that the rational use of disinfectants is critical to prevent poisoning ourselves, the fragile ecosystem and the world!
