Hands (and other animate surfaces) vs environmental (inanimate surfaces or fomites) .

Whilst stuck in isolation, the urge to reliably disinfect everything - from hands to door handles and aircon seems only natural.

Keep in mind: even in times of coronavirus the basics of chemistry and toxicology are still applicable. It is paramount to distinguish between disinfectants and disinfection techniques used on animate (hands, other body parts) and inanimate surfaces.

Whilst the most efficient (and economical) way to kill pathogens would be heating to pasteurising (72C for 15s) or sterilising levels (120-132C for 3-18 min), thermal disinfection methods are definitely

Chemistry behind disinfection:

Killing of pathogens at room temperature could be realistically achieved by:

1. denaturing of vital for pathogen survival biological polymers (proteins, cell wall compounds, RNA, DNA). The pathogens would be killed (or deactivated) when soluble in water biopolymers will become water insoluble when water is replaced with other solvent - mostly ethanol or isopropanol. The catch: alcohol (or other solvent) concentration needs to be at least 60% to efficiently denature pathogens, especially when contact times are short. The higher the concentration of alcohol - the more flammable and more toxic it becomes

2. Oxidising of biopolymers using strong oxidising agents - eg bleach or hydrogen peroxide.

The catch: bleach (chlorine-based) corrode and damage both animate and inanimate surfaces whilst too many pathogens have protective mechanisms against hydrogen peroxide

3. Chemical poisoning (benzalkonium chloride, phenoxyethanol etc). These actives mostly target specific areas of living cells (eg lipid layers of cell membrane) compromising cell permeability and causing leakage of cell content. The catch: the same toxicity to our own cells (ie irritations and allergies) and the cells of living creatures in aquatic reservoirs (shell fish etc).

Hands and other animate surfaces:

Q1. Hand wash or alcohol hand rub?

A. Of course handwash. By far more efficient and 5-10 times cheaper on per use basis than alcohol rubs. The US CDC is clear:

Hand sanitisers with at least 60% of alcohol should be used only "...if soap and water are not available". Handwashes are not only more efficient in decontaminating hands, but also (on per-use basis) are about 5-15 times cheaper

https://www.cdc.gov/handwashing/show-me-the-science-hand-sanitizer.html

Q2. When using hand wash, is antibacterial preferable?

A. Absolutely not. Hundreds of studies performed worldwide on popular in 1990s antibacterial handwashes had proven that there is no advantage of using antibacterial ones : at contact times and concentrations of actives any noticeable biocidal efficacy would be achieved after 8 hours(!!!).

Q3. If using alcohol rub, how much should I use?

A. All alcohol hand rubs are validated at 3 ml dose. An average general public use - 0.5-0.8ml. Definitely not enough to replace water on sweaty hands for reliable denaturing of biopolymers (and killing pathogens)

https://www.acsh.org/news/2017/01/10/you-arent-using-enough-hand-sanitizer-10717

Q4. 3 ml of alcohol rub seems like a lot. Why do I need so much?

A. The areas where most pathogens hide are cuticles, perionychium (skin over the sides of the nail) and hyponychium (area between the nail plate and fingertips).

To reach pathogens in these hard-to-access areas

(https://microbewiki.kenyon.edu/index.php/Human_Hands_and_Fingernails), one needs a lot of liquid. This is why as much as 3ml of alcohol rubs is required

Q5. Viscous or non-viscous alcohol rub?

A. The less viscous - the better. The higher the viscosity, the less chance to deliver alcohol to those cuticles and hard-to-reach areas.

Q6. Should I use antibacterial/sanitising hand wipes and towelettes to improve my hand hygiene?

A. Only if both hand wash and alcohol rubs are not available. The antibacterial hand wipes and towels are the least efficient and by far the most expensive option when compared to hand wash and alcohol rubs. The wipes deliver even less alcohol (equivalent of 0.2-0.4 ml) than under-dosed alcohol rub with very little chance to soak pathogens around cuticles. The biggest danger - providing false sense of safety

Q7. Should I use antibacterial/sanitising hand towels to wipe my hands?

A. These deliver hundreds times less antimicrobial actives than antibacterial handwashes and when used as expected have no benefit over standard cheap towels. I definitely agree with the main point (not the length :-) of the below presentation:

https://www.youtube.com/watch?v=inGNTjqNxl8

- antibacterial hand towels are plain dangerous for their ability to create superbugs and cause antibiotics resistance.

Inanimate (Environmental) surfaces.

Q1. What is more preferable: bleach (oxidising), denaturing agents or chemical disinfectant?

A. To rank these on efficacy vs cost basis (of actives):

- Oxidising agents are always preferable. If the surfaces are bleach-resistant and the smell is of no concern, definitely go for the 1:100 diluted with water household bleach.

- Alcohol and other denaturing agents-based disinfectants are 3-20 times more expensive (cannot be diluted), toxic and flammable. But can be used on nearly all household surfaces

- Chemical disinfectants with common approved actives pricewise are cost efficient and friendly to household surfaces. The problem with this group of products - when used at safe (i.e. very low) concentrations (e.g. less than 0.1% benzalkonium chloride) their pathogen killing efficacy is somewhat questionable. 99.9% reduction claim that you might find on many household disinfectants is (A) applicable only too well pre-cleaned surfaces and (b) not much of improvement on cleaning alone (99-99.5%).

To achieve half-decent disinfection of 99,99% and greater (The Australian TGA requires min 8-log reduction for hospital grade disinfectant) the actives should be used at 0.4-2%. Since the actives are quite toxic, the product label most likely will have scary red diamonds, warnings and requirements to wear respiratory protection and gloves when using these efficient products. But if you really want to disinfect your home or office, there is not too many options left.

Q2. Is there an option to create a self-sanitising surface? To keep it pathogen-free between cleaning.

A. There are tens of products on the market claiming bactericidal coatings and films lasting for days, months and even years.

Obviously, the common-sense 'when something sounds too good, most likely it is not' rule applies. A quick literature search on efficacy of organosilane - the most common active used for creating long lasting self-sanitising surfaces - returns a range from 'extremely efficacious' in lab-based trials to 'no efficacy at all' mostly tested in the clinical settings.

When the surface is rarely touched (low touch surfaces) between disinfection cycles - it really makes little difference whether it is sanitised or not.

When the surface is touched often (high-touch surfaces think of handrails, toilet flush or door knobs), the number of factors to consider becomes too overwhelming to standardise the side-by-side tests to compare the efficacy of bactericidal coatings: touched with clean or dirty hand, wetness (wet or dry), levels of dust in the room, applied pressure (woman, man, child, pet), sharpness of the touching object (sharp fingernail or soft skin), is the coating applied to vertical or horizontal surface etc.

There is good reason why the US EPA came up with a very stringent procedure (#01-1A) for validating such self-sanitising claims using alternative wet and dry abrasions. Still the pertinent factors - like dust in the room, UV exposure, applicable real-life abrasion challenges and many others are not addressed in the US EPA test methodology. We are here to help - offering a variety of the US EPA test modifications (validated, of course) to select the best self-sanitising solution for your application.

Dr Alex Sava