Does Blood on “Dirty” Instruments Interfere With the Effectiveness of Sterilization Technologies?

Background: Surgical instruments that enter sterile tissue should be sterile because microbial contamination could result in disease transmission. Despite careful surgical instrument reprocessing, surgeons and other healthcare personnel (HCP) describe cases in which surgical instruments have been contaminated with organic material (eg, blood). Although most of these cases are observed before the instrument reaches the patient, in some cases the contaminated instrument contaminates the sterile field, or rarely, the patient. In this study, we evaluated the robustness of sterilization technologies when spores and bacteria mixed with blood were placed on dirty (uncleaned) instruments. Methods: Dirty surgical instruments were inoculated with 1.5105 to 4.1107 spores or vegetative bacteria (MRSA, VRE or Mycobacterium terrae ) in the presence or absence of blood. The spores used were most resistant to the sterilization process tested (eg, Geobacillus stearothermophilus for steam and HPGP and Bacillus atrophaeus for ETO). Once the inoculum dried, the instruments were placed in a peel pouch and sterilized by steam sterilization, ethylene oxide (ETO), or hydrogen peroxide gas plasma (HPGP). These experiments are not representative of practice or manufacturer’s recommendations because cleaning must always precede sterilization. Results: Steam sterilization killed all the G. stearothermophilus spores and M. terrae when inoculated onto dirty instruments in the presence or absence of blood (Table 1). ETO failed to inactivate all test spores ( B. atrophaeus ) when inoculated onto dirty instruments (60% failure) and dirty instruments with blood (90% failure). ETO did kill the vegetative bacteria (MRSA, VRE) under the same 2 test conditions (ie, dirty instruments with and without blood). The failure rates for HPGP for G. stearothermophilus spores and MRSA were 60% and 40%, respectively, when mixed with blood on a dirty instrument. Conclusions: This investigation demonstrated that steam sterilization is the most robust sterilization process and is effective even when instruments were not cleaned and the test organisms ( G. stearothermophilus spores and MRSA) were mixed with blood. The low-temperature sterilization technologies tested (ie, ETO, HPGP) failed to inactivate the test spores but ETO did kill the test bacteria (ie, MRSA, VRE). These findings should assist HCP to assess the risk of infection to patients when potentially contaminated surgical instruments enter the st