Infection Control - Time-dependant Bacterial Air Contamination in the Operating Room

Intervention - In the evening before an elective surgery the sterile surgical goods will be prepared under calm circumstances with only 2 persons in the OR (intervention). Thereafter, the sterile goods will be protected with sterile covers and time pending surgery will be approximately 12 hours (intervention). The control is to prepare the sterile goods in the morning with more people in the OR (approximately 4-5 persons). Thereafter, the sterile goods will be protected with sterile covers (time pending surgery will be approximately one hour). For allocation, a computer-generated randomization list will be produced and an independent secretary will be arranging the printed notes showing the group assignment in ordered, sealed, non-transparent envelopes.

To measure the time pending surgery tables will be arrange with blood agar plates to measure the bacterial air contamination. There will be two tables, one protected with sterile covers and one left without protective covers (in both intervention- and control group).

Outcomes and materials - Primary outcome is bacterial growth isolated by aerobe and anaerobe blood agar plates (haematin agar medium 4.3% w/v [Colombia Blood Agar Base] supplemented with 6% w/v chocolatized defibrinated horse blood) and FAA plates (LAB 90 Fastidious Anaerobe Agar 4.6% w/v supplemented with 5% w/v defibrinated horse blood). Secondary outcome is surgical site infections with comparison of bacteria type.

Data collection - A total of 1260 blood agar plates will be used to capture bacterial air contamination. To capture differences in bacterial air contamination during different preparation conditions of the sterile goods, six agar plates (three haematin and three FAA) will be set on a table as the preparation begins. When preparation is complete the agar plates will be collected, by closing the lid of the agar plates. To measure the time-dependant bacterial air contamination pending surgery new agar plates (three haematin and three FAA) which will be set on tables for both intervention- and control group and covered with sterile drapes. To measure the effectiveness of sterile coverage from bacterial air contamination agar plates will be left uncovered pending surgery in both intervention- and control group. When preparing the patient for surgery the covers will be removed and all the plates will be collected by closing the lids.

Microbiology - The plates will be analysed at the Department of Laboratory Medicine, Clinical Microbiology, Örebro University Hospital, according to a specific study protocol. The haematin plates will be incubated at 36°C under aerobic conditions while the FAA plates will be incubated under anaerobic conditions (10% H2, 10% CO2, 80% N2) at 37°C. After 24 and 48 h of aerobic incubation and five days of anaerobic incubation, bacterial growth will be determined quantitatively by counting colony-forming units per plate. The isolates will be identified by routine diagnostic procedures and determined to species level via matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (Microflex LT and Biotyper 3.1, Bruker Daltonik, Bremen, Germany).