To reduce infection risk, keep surgical trays closed - Academy News at the 2007 AAOS Annual Meeting

To reduce infection risk, keep surgical trays closed and covered

By Jennie McKee

How long can a sterile tray be exposed to the open environment before contamination risk becomes unacceptable? Not very long, according to podium presentation 321,“Time-dependent contamination of opened sterile trays.”

Researchers found “culture positivity correlated directly with the time of open exposure for uncovered trays,” with a 22 percent culture positive rate after two hours and a 30 percent culture positive rate after four hours. Traffic in and out of the operating room (OR) had no impact on contamination risk. Simple, practical sterile towel coverage of surgical trays, however, significantly reduced contamination risk.

Surgical site infection remains an important focus in the practice of orthopaedic surgery. “While we often take great care in addressing those factors perceived as readily modifiable,” noted the authors, “others may perhaps be overlooked, thought to be uncontrollable or taken for granted as already being ideal. Specifically, the absolute sterility of surgical trays and the instruments they contain is often assumed. Additionally, the contribution of an operating room’s air quality to surgical infection rates is thought to be minimal or perhaps even inconsequential given routine use of positive or laminar airflow systems.”

Three groups studied

Sterile trays may be opened but not immediately used in situations such as a delay to the start of an operation or multiple procedures performed in the same operative setting. The researchers sought to determine the time to first contamination and the rate of time-dependent contamination for opened sterile trays in a controlled OR environment.

Researchers opened a total of 45 sterile trays in a positive-air flow OR. Trays were randomly assigned to one of three groups. The first group of 15 trays were placed in a locked OR where no doors were opened during the study period. The second group (uncovered, traffic) was identical to the first, with the addition of single-person traffic flowing in and out of the OR from a non-sterile corridor every 10 minutes. The final 15 trays were placed in a locked OR and were immediately covered with a sterile surgical towel after opening. All trays were opened using sterile technique and were exposed for four hours.

Researchers obtained tray cultures immediately upon opening and every 30 minutes thereafter for the four-hour study period. Researchers also regularly assessed air quality control, using bacterial and fungal plates. Two study participants were involved with each tray.

Because three (10 percent) of the 30 uncovered trays were immediately contaminated when opened, they were eliminated from the study. Uncovered trays became contaminated at the following rates:

  • 4 percent (1 of 27) at 30 minutes
  • 15 percent (4 of 27) at one hour
  • 22 percent (6 of 27) at two hours
  • 26 percent (7 of 27) at three hours
  • 30 percent (8 of 27) at four hours

Skin flora most common contaminant

“Of the positive cultures, 44 percent were coagulase negative staphylococcus, 22 percent corynebacterium, 11 percent alpha streptococcus, 11 percent bacillus species, 6 percent micrococcus and 6 percent moraxella species,” noted the researchers. “One of eight (12 percent) contaminated trays was polymicrobial. There was no difference in mean survival time (p = 0.47) or contamination rate (p = 0.69) between the uncovered trays with traffic versus those without traffic.”

To the contrary, the 15 covered trays experienced no contamination over the four-hour testing period. “Our results demonstrate that common skin flora appear to be the predominant source of contamination for exposed trays and instruments in the OR...implicating people as the most likely source of intraoperative tray contamination.”


As a result of this study, researchers recommend that “sterile trays should not be opened until specifically needed during the procedure. However, if a tray is opened but not immediately used, sterile towel coverage is recommended to minimize exposure to environmental contaminants.”

The lead researcher for Paper 321 is Michael J. Prayson, MD, of Dayton, Ohio. Additional researchers include Alison L. Manternach, RN, MSA and Marilyn S. Palcic, PA-C; David J. Dalstrom, MD; Indresh enkatarayappa, MD, and Beth A. Heyse, RN, also of Dayton, Ohio. Support for this study was provided by a grant from the Miami Valley Hospital Foundation and the Association of periOperative Registered Nurses.

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