Surgery and instruments: more detail

What does a validated 134 C cycle achieve?

Schwenke and colleagues addressed a gap that had sat under instrument policy for years. Most sterilisation methods had been validated against scrapie, which is generally less heat resistant than human prions, so the margin for human agents was unmeasured.

They exposed several strains to steam sterilisation at 134 C for different holding times and measured residual seeding activity by protein misfolding cyclic amplification. The hamster scrapie strain 263K was the least resistant, with no seeding activity after 1.5 minutes. Sporadic CJD of the VV2 subtype still showed activity after 3 minutes and none detectable after 5 minutes. Variant CJD was the most stable, with some activity remaining after 18 minutes.

Their conclusion supports the validated 5 minute cycle at 134 C for instruments that have contacted high risk tissue, under two stated conditions. No fixing chemical disinfectant may have been applied before sterilisation, and cleaning must have reduced the protein load to less than 100 micrograms per instrument.

Those two conditions carry most of the practical weight. A fixing disinfectant used early in a decontamination pathway can defeat the cycle that follows, and the protein limit makes the quality of the cleaning step, not the autoclave setting, the thing that determines the outcome.

Two limits should be read alongside the result. Seeding activity measured by amplification is not the same as infectivity in an animal, so absence of detectable seeding is not a demonstration of sterility. And the variant CJD result means that no routine cycle in ordinary use can be assumed to deal with that agent.

Why quarantine rather than reprocessing?

Because the measurements above do not support reprocessing for the highest risk combinations. UK guidance therefore separates instruments by the tissue they touched and the certainty of the diagnosis.

Instruments used on high or medium risk tissue in a definite or probable case are incinerated or quarantined for exclusive reuse on the same patient. Instruments used where the diagnosis is still pending are quarantined until it is settled, which is also the logic behind the CDC’s instruction that neurosurgical instruments used on a patient of unknown status be reprocessed as though CJD were suspected. Instruments used only on low risk tissue are reprocessed to best practice and returned to use.

The CDC’s own position on heat-resistant instruments that have contacted high infectivity tissue is that destruction is the safest option while acknowledging it may be impractical or costly, and it sets out three combinations of sodium hydroxide or sodium hypochlorite with autoclaving where instruments are reused. It also reports that in testing by the US regulator, sodium hydroxide soaking damaged instruments least, while hypochlorite severely damaged some.

Which documents govern which step?

The UK guidance is a set maintained by the Advisory Committee on Dangerous Pathogens’ subgroup on transmissible spongiform encephalopathy, first published in November 2012 and revised in parts since.

Annex A1 states how infectivity is distributed across human tissues and body fluids, and is the document behind any local statement that a procedure is low risk. Annex C covers decontamination and waste disposal principles. Annex E covers quarantining of surgical instruments. Annex I gives the protocol for instruments and tissues from brain biopsies in patients with progressive neurological disorders. Annex J covers the assessment before surgery or endoscopy that identifies patients with or at risk of CJD, with explanatory diagrams added in 2017.

Specialty documents sit beside these: endoscopy, pathology laboratory handling, ophthalmology, and general surgery and liver transplantation. There is also a one-page alert to urological surgeons about equipment for transrectal prostate biopsy in patients at risk of variant CJD. A service that reads only the main infection control document can miss the item that applies to its own list.

Naming the annex is usually what resolves a local disagreement, because most disputes are about which risk category a procedure falls into rather than about what the precaution should then be.

Where does nasal and ocular tissue fit?

This is the area where published findings and written guidance are least aligned. A 2014 report on olfactory mucosa brushings noted that brushings contained more prion seeds than cerebrospinal fluid, which raises questions about nasal secretions and about the instruments used to collect them. That observation reached the research literature well before any revision of routine endoscopy practice, and the sources opened here do not show it changing instrument categories.

Eye tissue is already treated as high infectivity, and UK guidance carries a substantial separate annex on ophthalmology for that reason.

What is not settled

The strongest statement the sterilisation work supports is about seeding activity under controlled laboratory conditions with a measured protein load. Real decontamination pathways involve transport, delay, variable cleaning and sometimes chemical disinfection, and no published study opened here measures the end to end result in a working hospital.

The claim a clinician should check first, before relying on this page in a local policy, is the 100 microgram protein limit: it is the condition on which the 5 minute cycle’s adequacy rests, and whether a given cleaning process meets it is a local measurement rather than something the published study establishes.

Care settings covers ward and community care, and official documents are tracked in the regulations atlas.