Bacterial contamination of covered versus non-covered plates in a sterile operating room in an equine referral center.

This study found that covering surgical instruments with a sterile towel reduced the number of airborne bacteria that settled on nearby plates during equine orthopedic surgeries over 30–120 minutes. Most bacteria were gram-positive cocci and many were not the species typically implicated in equine surgical site infections, so the direct clinical impact remains uncertain.

Clinical problem and study objective

• Surgical site infections (SSI) are a frequent and serious complication after equine orthopedic procedures, increasing both morbidity and mortality.
• Teams sometimes open instrument packs early (early opening of surgical packs, EOSP), potentially exposing instruments to airborne contaminants.
• The study asked whether simply covering instruments with a sterile surgical towel during EOSP decreases airborne bacterial contamination.

Study design and methods

• Setting: A sterile operating room in an equine referral center during six orthopedic surgeries.
• Comparator: Blood agar plates (BAP) placed on sterile instrument tables were assigned to two conditions:
  • Non-covered: plates left exposed to the air.
  • Covered: plates shielded with a sterile huck (surgical) towel.
• Replication and timing: Plates were tested in triplicate at each time point and condition during each procedure; exposure durations were 0, 30, 60, 90, and 120 minutes.
• Microbiology:
  • Colony counts (total colonies per plate) were recorded at each time point.
  • Bacterial speciation was performed on the 120-minute plates to identify common organisms present.
• Analysis: Covered versus non-covered counts were compared; significance was reported at p < 0.01 for specified time points.

Key results

• Across 30–120 minutes, non-covered plates accumulated more bacterial colonies than covered plates, with statistically significant differences (p < 0.01) at:
  • 30 minutes: non-covered mean 7.9 colonies (± 7.2 SD).
  • 60 minutes: non-covered mean 11 (± 7.9).
  • 90 minutes: non-covered mean 16.7 (± 11.3).
  • 120 minutes: non-covered mean 20.3 (± 14.7).
• Variability was substantial (large standard deviations), but the consistent direction favored covering.
• Bacterial speciation at 120 minutes showed gram-positive cocci predominance; many identified species are not commonly reported causes of equine postoperative SSI.

Interpretation and implications

• Covering instruments with a sterile towel reduces the number of airborne bacteria settling on nearby surfaces during the first 2 hours after opening—precisely the period when EOSP could pose a risk.
• The organisms sampled from the air were largely gram-positive cocci (for example, environmental or skin-associated aerobes), which may reflect human traffic and skin shedding rather than typical equine SSI pathogens.
• Because environmental settle plate counts are a proxy and not a direct measure of instrument contamination or clinical infection, the observed reduction in colonies suggests, but does not prove, a reduction in SSI risk.

Strengths of the study

• Practical, easy-to-implement intervention (a sterile towel) tested under real operative conditions during actual equine surgeries.
• Paired comparison of covered versus non-covered plates in the same operating environment improves internal validity by controlling for case-specific conditions.
• Multiple time points capture the time-dependent accumulation of airborne contamination.

Limitations and potential sources of bias

• The abstract does not report colony counts for the covered plates, limiting estimation of absolute and relative effect sizes.
• Speciation was performed only at 120 minutes, so the microbial profile at earlier intervals is unknown.
• Settle plates reflect passive deposition and may underestimate small aerosolized particles or turbulence-driven exposure; they are a surrogate for instrument contamination, not a direct measure.
• Operating room factors (personnel movement, door openings, ventilation patterns, location on the instrument table) may influence counts and are not detailed.
• The link between reduced airborne colonies and actual SSI in horses was not evaluated; many identified species were not typical SSI pathogens.

Practical takeaways for equine surgical teams

• When EOSP is unavoidable, covering opened instruments with a sterile huck towel or drape is a low-cost, low-effort step that likely reduces airborne bacterial deposition during the case.
• Maintain other basic controls: minimize door openings and traffic, ensure proper ventilation/airflow, and keep nonessential items off instrument tables.
• Prioritize timely opening of instruments to reduce exposure duration whenever feasible.

How to place these findings in context

• The decline in airborne colony counts with covering is biologically plausible and consistent with general aseptic principles.
• The clinical significance depends on whether the reduced environmental burden translates into fewer SSIs, particularly from pathogens relevant to equine orthopedic infections.
• Even if environmental organisms differ from common SSI pathogens, any reduction in overall bioburden may lower the chance of contamination events.

Future research directions

• Prospective studies correlating environmental counts, instrument contamination, and equine SSI outcomes to establish a causal chain.
• Comparisons of different covering materials (towel versus full sterile drape) and techniques (continuous versus intermittent covering) on contamination and workflow.
• Evaluation of other modifiable OR factors (ventilation rates, traffic patterns) alongside covering to quantify additive effects.
• Pathogen-focused monitoring (including earlier time points) to determine whether covering preferentially reduces clinically important organisms.