Design: Blinded, sham-controlled cluster-crossover randomised trial, stopped for futility
Population: 107,334 analysed operations in 68 operating rooms; 58,938 inpatients
Primary outcome: 30-day composite of wound infection, infection-related complication or death (inpatients)
Effect: 8.1% active vs 8.2% sham; OR 0.98 (95% CI 0.92–1.05)

ORACLE was a cluster-crossover trial: 68 operating rooms were randomised in four-week blocks to active supplemental air sterilisation or an identical-looking sham. Patients, clinicians and investigators were all blinded, and nothing else about care was prescribed. The primary outcome was a 30-day composite of surgical wound infection, infection-related complications or death after inpatient surgery of at least an hour.

The trial enrolled 110,538 operations and stopped at the third interim analysis for futility. In inpatients, the composite occurred in 8.1% with active and 8.2% with sham purification (OR 0.98, 95% CI 0.92–1.05). Results across all patients were the same, and did not change over time.

With this many patients and full blinding, a meaningful benefit is very unlikely. The trial was funded by the device maker, which approved the protocol but was not involved in analysis. The finding does not concern standard theatre ventilation, which remains essential.

In practice: buying supplemental air purifiers is unlikely to reduce infection. Effort is better directed at measures that limit direct wound contamination — timely prophylaxis, skin preparation, normothermia, glucose control and theatre discipline.

Do not invest in supplemental theatre air purifiers to reduce surgical infection.
Maintain standard theatre ventilation and air-change requirements.
Focus on antibiotic timing, skin preparation, normothermia and glucose control.
Limit theatre traffic and door opening during operations.

Why it matters

It answers, with over 100,000 blinded operations, whether add-on air cleaners earn their cost.

The statistics, in plain English

An interval of 0.92 to 1.05 is narrow and centred on no effect, so even a small benefit (more than about an 8% reduction in odds) is unlikely. Stopping for futility means more patients would not have changed the answer.