Time-related changes in bacterial air contamination of sterile covered items in operating rooms: a systematic review and meta-analysis

Clinical Snapshot

Key Findings

• P Value: p = 0.176 for CFU count; p = 0.108 for mean CFU values

• Effect Size: Time explains only 7-8.5% of CFU variation (R² = 0.070-0.085)

• Primary Outcome: Colony forming units (CFU) over time for covered sterile items

• Nnt Or Sensitivity: No statistically significant linear association between time and bacterial contamination when sterile covers used

• Confidence Interval: CFU count: -1.319 < β < 4.863; Mean CFU: 0.191 < β < 0.420

Clinical Application

Highly feasible - supports current practice of advance preparation of covered sterile items Aligns with ACORN standards for perioperative nursing and TGA guidelines for sterile medical devices. Supports efficient OR utilisation consistent with Australian healthcare efficiency initiatives Operating room staff, sterile processing departments, infection control teams

Abstract

BACKGROUND: There is still only limited evidence regarding how bacterial air contamination of sterile items changes over time in the operating room, even when protected by sterile covers. This review aimed to synthesize the available data to inform safe handling and preparation of sterile equipment. METHODS: A systematic search was conducted for controlled studies that assessed time-related bacterial contamination of covered sterile items in operating rooms and that reported the outcome as colony forming units (CFU) measured at two or more time points, generating distinct timelines. Six databases were searched from inception to 1 September 2025: Ovid MEDLINE, the Cochrane Central Register of Controlled Trials, CINAHL, the Cochrane Database of Systematic Reviews, Embase, and Web of Science. A meta-analysis was performed using linear regression with CFU as the dependent variable and time (minutes) as the independent variable. The review followed PRISMA guidelines and was registered in PROSPERO (CRD420251018280). RESULTS: Five timelines from four studies evaluating CFU counts yielded an R2 of 0.085, indicating that time explained 8.5% of CFU variation. Similarly, analysis of eight timelines from four studies assessing mean CFU values produced an R2 of 0.070, attributing 7% of variation to time. Neither analysis demonstrated a statistically significant linear association between time and CFU count (p = 0.176, CI: -1.319 < β < 4.863) or mean CFU values (p = 0.108, CI: 0.191 < β < 0.420) when sterile covers were used. Three additional timelines excluded from the meta-analysis showed mixed results: two indicated a positive association, while one showed no relationship. CONCLUSIONS: Time has only a modest impact on bacterial contamination of sterile items when protective covers are used, with minimal increases in CFU over different waiting periods. Clinically, this confirms that properly covered sterile items can be prepared in advance without compromising microbial safety, thus supporting efficient operating room organization and workflow. These findings reinforce the effectiveness of sterile covers as a key measure to reduce the risk of surgical site infections and ensure the safe handling of sterile equipment. Although covered storage appears safe, minimizing unnecessary waiting time, even with coverage, is good clinical practice.

References

1. 1.Wistrand, C., Westerdahl, E., & Sundqvist, A. S. (2026). Time-related changes in bacterial air contamination of sterile covered items in operating rooms: a systematic review and meta-analysis. Antimicrobial Resistance and Infection Control. https://doi.org/10.1302/0301-620X.78B5.0780835