Disinfection and Sterilisation — Questions

Spaulding sorts items by what they touch, and each category maps to a level of pathogen elimination with a characteristic procedure or agent.

• Sterilisation (critical items entering sterile tissue): steam autoclaving is the standard, with ethylene oxide or hydrogen peroxide gas plasma for heat-sensitive items.
• High-level disinfection (semi-critical items touching mucous membranes): a chemical high-level disinfectant such as glutaraldehyde, ortho-phthalaldehyde (OPA) or peracetic acid.
• Low-level disinfection (non-critical items touching intact skin): an environmental disinfectant such as a quaternary ammonium compound or 60 to 90% alcohol.

An item that touches mucous membranes but not sterile tissue is semi-critical and needs at least high-level disinfection. After disinfection it is rinsed, ideally with sterile water, to avoid recontamination.

It is neither critical (no entry into sterile tissue) nor non-critical (it exceeds intact-skin contact).

Glutaraldehyde coagulates blood and fixes tissue to surfaces, so instruments must be thoroughly cleaned first. It also irritates the airway and can cause colitis if inadequately rinsed.

It is kind to materials rather than corrosive, is broadly virucidal, and does not bleach fabric.

Candida auris persists on surfaces and resists some routine disinfectants, so a hospital disinfectant effective against Clostridioides difficile spores is recommended for its rooms. Chlorine, accelerated hydrogen peroxide and quaternary-alcohol products inactivate it rapidly.

Agents chosen only for enveloped viruses or ordinary vegetative bacteria may not clear this hardy yeast.

Quaternary ammonium compounds inactivate enveloped viruses but not the small non-enveloped viruses, so norovirus can survive a routine surface wipe. This is why agent choice matters for enteric-virus outbreaks.

Influenza, human immunodeficiency virus, herpes simplex virus and the coronavirus are all enveloped and readily inactivated.

Contaminated endoscopes have caused more healthcare-associated outbreaks than any other medical device, because their long narrow channels trap soil and resist inspection. Meticulous cleaning, disinfection, rinsing, drying and vertical storage are all required.

They are reusable semi-critical items needing high-level disinfection, not gas sterilisation, and can transmit bacteria, viruses and fungi.

Ethylene oxide is flammable and a known human carcinogen, so residual gas must be driven off by aeration before an item is safe to use. This makes each cycle slow.

It is in fact highly penetrating and sporicidal, and it is not corrosive to steel in the way described.

High-level disinfection kills all microorganisms except large numbers of bacterial spores. That single exception is what separates it from sterilisation.

Viruses, vegetative bacteria, mycobacteria and fungi are all within its range.

Brain, spinal cord and eye are the high-risk tissues that, from a patient with known or suspected prion disease, trigger special reprocessing of critical or semi-critical instruments. The instrument is kept moist, then decontaminated by sodium hydroxide with autoclaving or extended steam at up to 134 °C.

Liver, kidney, lung and bone marrow are not designated high-risk tissues for prion transmission.

Spaulding graded reprocessing by the infection risk of what an item touches, not by what the item is made of. Contact with sterile tissue, mucous membranes or intact skin sets the required level.

Material, cost, ward and warranty are irrelevant to the classification.

Ortho-phthalaldehyde is contraindicated for cystoscopes, following anaphylactic reactions in bladder-cancer patients undergoing repeated cystoscopy. It otherwise acts fast and needs no activation, but it stains proteins and skin grey.

The other endoscopes listed are not subject to this specific contraindication.

A duodenoscope reaches the biliary tree through the duodenum, so it effectively enters sterile tissue and meets the definition of a critical item that should be sterilised. More than twenty-five outbreaks of multidrug-resistant organisms, several despite correct high-level disinfection, drove this shift.

Treating it as semi-critical, non-critical or non-invasive underestimates the risk, and intermediate is not a Spaulding category.

Sterilisation destroys all microbial life, including bacterial spores, whereas high-level disinfection kills everything except large numbers of spores. Sporicidal activity is the dividing line between the two.

Heat stability, the site contacted, the item type and the need for cleaning do not define the distinction.

The hospital environment often carries SARS-CoV-2 genetic material but rarely viable virus, and the fomite route plays only a limited part, so an ordinary hospital disinfectant from the regulator’s emerging-viral-pathogen list, applied to high-touch surfaces, is sufficient.

Sterilising all surfaces is unnecessary, bleach is not uniquely required, fomites are not the main route, and surfaces still need routine disinfection.

No-touch technologies supplement, but do not replace, manual cleaning, and are reserved for terminal decontamination of rooms that housed patients with persistent pathogens. They act only on surfaces a device can reach.

They neither sterilise a whole room nor are used on skin, and they do more than remove dust.

A large blood spill is decontaminated with a 1:10 dilution of household bleach, and a small spill with 1:100. Hypochlorite is fast, cheap and broadly virucidal, including against non-enveloped viruses.

More dilute solutions are too weak for a large spill, and undiluted bleach is unnecessary and more corrosive.

A surgical implant enters sterile tissue, making it a critical item that must be sterile. Critical items are bought sterile or steam-sterilised where the materials allow.

A laryngoscope blade is semi-critical, while a cuff, stethoscope and bedpan are non-critical.

Hydrogen peroxide gas plasma cannot process cellulose materials such as paper and linen, and it has lumen-length limits. It works below 50 °C with no toxic residue and no aeration.

Metal and synthetic-polymer items are compatible with the process.

The lipid envelope is the vulnerability: enveloped viruses are the least resistant, as alcohols, hypochlorite and even quaternary ammonium compounds disrupt the envelope. Human immunodeficiency virus, hepatitis B virus and influenza are all easy targets.

Non-enveloped viruses are harder, not easier, to inactivate, and genome type and mutation rate are irrelevant to chemical susceptibility.

Steam under pressure is the most widely used and dependable method: non-toxic, inexpensive, rapidly sporicidal and well penetrating. It runs at 121 °C or 132 °C and is least affected by organic soil.

The low-temperature and chemical methods exist mainly for heat-sensitive items, and ultraviolet does not sterilise instruments.

Alcohol at 60 to 90% is rapidly bactericidal, tuberculocidal and virucidal but is not sporicidal, so it cannot sterilise. It also evaporates quickly, making a long wet contact time hard to maintain.

Staining, tissue fixation and light inactivation are properties of other agents, not alcohol.

Residual organic soil both physically shields microorganisms and chemically inactivates many germicides, so cleaning is the indispensable first step. Soil left to dry becomes far harder to remove, so instruments are kept moist until cleaned.

Cleaning neither sterilises on its own nor replaces disinfection, and dried blood impairs rather than aids the process.