RCT of 110,538 Surgeries Finds Operating Room Air Purifiers Do Not Reduce Surgical Site Infections

The ORACLE trial, published in Anesthesiology, installed paired active and inactive air-purification units in 68 rooms and switched them every four weeks in a double-blind design spanning several years. More than 110,000 procedures were analyzed for the primary endpoints of surgical site infection, postoperative complications, and mortality. No between-period differences emerged, indicating that airborne bacterial load in modern operating rooms is not a dominant driver of these outcomes.

Absolute infection rates remained in the 1-3% range reported by CDC surveillance regardless of filtration status, with relative risk ratios indistinguishable from 1.0. This large-scale interventional evidence aligns with smaller prior observational data suggesting that direct sources—patient skin flora, intestinal spillage, or instrument contamination—account for most events. Hospitals investing in high-cost laminar-flow or UV systems may therefore see limited return.

The trial design rules out meaningful benefit under sterile OR conditions but leaves open questions for less controlled environments such as wards or ICUs. Next studies should power similar blinded comparisons outside the operating room and measure both infection rates and direct contamination events to identify high-yield prevention targets.

This RCT provides strong causal evidence against routine OR air-purification upgrades yet cannot exclude niche benefits in non-sterile settings; adequately powered trials in those environments are required before broader policy changes.