Spore-strip failure in a 25-bed nursing home autoclave
A 25-bed nursing home in a district town runs its own central sterile services department. Dressing packs are wrapped in two layers of cotton cloth, loaded into a horizontal autoclave and processed at 121 °C, 15 psi for 20 minutes. On Monday the technician adds an extra pack to an already full chamber and closes the door without checking that all air has been removed. The pressure gauge reads 15 psi, but the dial thermometer records 118 °C. The biological indicator, a Geobacillus stearothermophilus spore strip placed in the middle of the load, turns soyabean casein digest broth turbid after 48 hours at 56 °C. The same autoclave is also used for a flexible fibreoptic endoscope, because the nursing home has no other equipment. In the treatment room a 2-litre bottle of 2% glutaraldehyde has been topped up and reused for three weeks, and two nurses complain of eye and throat irritation.
1. The spore strip grew. Explain the most likely reason for the failure and state exactly what must be done with Monday's packs before any of them is opened on a patient.
Read the worked answer
Why it failed. The decisive clue is the pair of readings: 15 psi on the gauge but only 118 °C on the thermometer. Saturated steam at 15 psi gauge is 121 °C, so any temperature below that means the chamber pressure is partly made up of air, not steam. Trapped air forms an insulating blanket, the steam is not saturated, and moist heat at 118 °C for 20 minutes does not give the required kill. Overloading and a tightly packed chamber made it worse, because steam could not penetrate to the middle of the load where the strip sat.
What to do.
- Treat the whole run as unsterile. Quarantine every pack, and recall any pack already sent to the wards.
- Do not simply re-run the load and hope; correct the cause first (air removal, load size, pack wrapping, door seal).
- After repair, re-validate with three consecutive biological indicator runs, each negative, plus a Bowie–Dick test for air removal, before routine use resumes.
- Record the failure, the recall and the validation in the CSSD register; a single negative strip after a change is not enough evidence.
2. Explain why the endoscope should not be put in this autoclave, and describe what should replace autoclaving in a facility of this size.
Read the worked answer
Why not. A flexible endoscope contains cemented lens assemblies, optical fibres and polymer seals that deform or crack at 121 °C; the instrument would be destroyed, and the damaged channels would then be impossible to clean. Heat is not the only issue - the instrument cannot be wrapped and stored sterile because its channels are re-contaminated the moment it is handled.
What replaces it. High-level disinfection (HLD) after meticulous manual cleaning:
- Dismantle valves, brush all channels, flush with detergent and water; cleaning removes the biofilm and organic load without which any chemical fails.
- Immerse completely in 2% glutaraldehyde for about 20 minutes at 20 °C for HLD (sterilization needs many hours and is not the practical standard for flexible scopes), or use OPA/peracetic acid in an automated processor.
- Check the disinfectant with a minimum effective concentration strip before each session, discard when it fails or at the manufacturer's reuse limit, keep the tray covered, and ventilate the room.
- The eye and throat irritation is a warning that the glutaraldehyde vapour is escaping; staff need gloves, eye protection and a closed container, and the topped-up three-week-old bottle should be discarded.
3. Draw up the routine monitoring plan that would have caught this failure earlier.
Read the worked answer
A sterilizer is judged by three independent lines of evidence, and all three must agree before a load is released.
1. Mechanical monitoring (every load): read and record pressure, temperature and time against the specified cycle. The 118 °C/15 psi mismatch would have been visible on the chart at once, so the chart recorder and pen must be working every day.
2. Chemical indicators (every pack): autoclave tape or an internal indicator strip changes colour only if the pack itself reached the required conditions. An external label alone proves nothing about the centre of the pack. For a pre-vacuum cycle, a Bowie–Dick test is run at the start of each day to prove air removal.
3. Biological monitoring: a Geobacillus stearothermophilus spore strip in a representative pack, incubated with an unprocessed control, at least weekly and after every repair, with written results. A positive result triggers quarantine of all loads back to the last negative test.
The plan must also cover loading discipline (no overfilling), pack thickness, drying time, and a signed release record, so that a load is never released on the operator's impression alone.