The OR: A Prime Target for Pathogens

Surgical-site infections invariably involve surgeons, operating room (OR) nurses, sterilization of equipment, and so forth. Anesthesiologists, nurse anesthetists, and other anesthesia practitioners also contribute substantially to the transmission of pathogens.

For context, incidences of surgical-site infections differ based on inclusion criteria and lengths of patient follow‑up.¹ For example, measured incidences have been 7.7% for inpatient surgery based on 60-day follow-ups,² 5.5% for inpatient surgery based on 30-day follow-ups,³ and 3.7% for inpatient and outpatient hospital surgery using billing codes for diagnosis.⁴ A randomized trial showed that perioperative transmission of ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species) can be reduced, which reduces surgical-site infections.² Prospective observational study then showed the strategy can be implemented throughout a multidisciplinary surgical suite.⁵ A bundle of interventions (Table^6,7) are combined with feedback to clinicians about intraoperative bacterial transmission.^2,5

Pathogen transmission is measured using Staphylococcus aureus as a marker. For example, investigators at Georgetown were sent boxes with swabs, tubes, etc, and once used, they were returned for culturing and analysis.⁸ The investigators studied the time it took to perform sampling using the kits.8 Anesthesia assistants essentially opened sterile swabs, swabbed anesthesia-machine valves, patient axilla, stopcock lumens, etc.⁸ There were 13 sites per case, 6 at the start and 7 at the end.⁸

Sampling was done for successive cases in the same OR on the same day (“case pairs”)^2,9,10. An example of transmission within a case was from the nasopharynx of the patient at the start of the case to the anesthesiologist’s hands sometime by the end of the case.¹⁰ An example of transmission between cases was from the nurse anesthetist’s hands at the start of the first case to the nasopharynx of the second patient (when sampled after induction), observed on the nurse anesthetist’s hands again at end of second case and also on the anesthesia equipment at the end of the second case.¹⁰ From the study, sampling time averaged 3.4 minutes at the start of each case and 4.4 minutes at the end of each case—the total significantly briefer than 10 minutes.8 The cases from which sampling is done generally are 3.3 to 4.8 hours long⁴; therefore, circulating nurses can obtain the samples. If this is done, instead, by anesthesia technicians or infection preventionists, add the time waiting for patient induction and to be present at the end of surgery.⁸

The primary end point of the randomized trial and observational effectiveness study was S aureus transmission. For the randomized trial, 19 surgeons and their patients were randomized to usual care or infection-control bundle with feedback.² Patients with transmission had 6-fold greater risk of surgical-site infection (P = .007). Treatment reduced the incidence of transmission (incidence risk ratio [IRR], 0.56; P < .001) and infection (HR, 0.12; P = .004).² For the effectiveness study, 804 patients were observed months before and after the infection-control program, including transmission feedback.⁵ Optimization reduced the incidence of transmission (IRR, 0.39; P < .001) and infection (IRR, 0.42; P = .009).⁵

Monitoring and feedback using S aureus transmission complements reporting of surgical-site infections. Although the incidence of surgical-site infection varies more than 10-fold among surgical procedures,¹¹ consistently there are no covariates for transmission: not the procedure, not surgical duration, not a dirty wound, not patient characteristics.⁵ Also, the incidence of S aureus transmission is many-fold higher than resulting surgical-site infections. Both factors make feedback about transmission easier to explain (Table).

For a hospital to begin checking S aureus transmission, the first decision to make is which ORs to sample. Some fundamental characteristics of surgical suites are relevant.^11,12 Some ORs have many more cases per week than others, principally because some rooms’ cases take much longer than other rooms’ cases.¹² Also, surgical specialties are distributed unequally among ORs (eg, rooms used preferentially for one specialty versus another), and average case urgency differs among rooms, as does the American Society of Anesthesiologists’ physical status score.¹² The implications are substantial.^4,11,12 From a study of 57 ORs in a large teaching hospital, the 20% of ORs with the most surgical-site infections accounted for 44% of S aureus transmission, whereas the 20% with the least infections accounted for 5% of S aureus transmission.¹² The 10% of specialty and OR combinations with the most surgical-site infections accounted for 76% S aureus transmission, whereas 47% of operating rooms had zero observed infections.¹² That latter result is important for purposes of monitoring S aureus transmission within and between case pairs. Use your surgical-site infection data—not for regular feedback, but rather, to choose a few specialty-OR combinations to target for monitoring and intervention.¹²

Pathogens likely are transmitted intraoperatively in all ORs.^2,5 What differs are probabilities of transmission resulting in surgical-site infection.^4,12 Many hospitals report surgical-site infections per month in control charts. With 3 years of data, when plotted by OR, there was no paired association with cases per month.⁴ The reason: Although ORs with more overall minutes per case (ie, longer) had greater incidence of infection (P<.001), those ORs had far fewer cases per day (P<.001).⁴

In other words, the ORs with very long cases (> 4.8 hours) have the greatest incidence of surgical-site infections, yet on many days, have only one case.⁴ In contrast, the ORs with cases averaging 3.3 to 4.8 hours in length have cases long enough for greater risk of surgical-site infection and usually 2 or 3 cases per day.⁴ In general, those are the ORs to target to prevent pathogen transmission. Beneficially, when monitoring S aureus transmission using the few specialty-OR combinations with the most infections, applying the bundle of infection prevention interventions (Table) and monitoring S aureus transmission can be net cost savings.⁴

Having selected the ORs for monitoring S aureus transmission, the next related question is how many case pairs to sample. From the randomized trial, we have a typical incidence for transmission in the usual care group and a corresponding low incidence achieved with infection prevention bundle and feedback.² Using those 2 incidences and applying statistical power analysis, the sample size would be 25 case pairs.13 For example, suppose that the targets for infection prevention were the 3 ORs of one specialty.⁴ Then the cases studied could be the first and second cases of the day in each room for 2 weeks. That would potentially give 30 case pairs, but cases occasionally cancel, all sampling cannot be completed, and so forth. After implementation (Table), the sample sizes for S aureus transmission need not be as large as for the randomized trial and observational study.^2,5,13 A reasonable choice for feedback is to use culture results from another 75 case pairs.¹³ This information on sample size helps infection preventionists have context on number of surgical cases for sampling so that they can help the anesthesiologists and nurse anesthetists (and surgeons, OR nurses, and other anesthesia practitioners) know what to change to reduce transmission of the intraoperative bacterial pathogens.

In conclusion, substantial understanding exists about how OR pathogens cause surgical-site infections. It is known that the processes involved include not only contaminated wounds and resistance to otherwise appropriate antibiotics, but also bacterial transmission including the anesthesia environment.^2,5 Feedback to anesthesia practitioners contributes to reduced surgical-site infections because that transmission can be mitigated with basic measures (Table).^2,5 There is considerable understanding of why and how best to use S aureus transmission as a marker of transmission for the purpose of feedback.^4,8,9,11-13

1. Taylor JS, Marten CA, Potts KA, et al. What is the real rate of surgical site infection? Oncol Pract. 2016;12(10):e878-e883. doi:10.1200/JOP.2016.011759
2. Loftus RW, Dexter F, Goodheart MJ, et al. The effect of improving basic preventive measures in the perioperative arena on Staphylococcus aureus transmission and surgical site infections: a randomized clinical trial. JAMA Netw Open. 2020;3(3):e201934. doi:10.1001/jamanetworkopen.2020.1934
3. Petrosyan Y, Thavorn K, Maclure M, et al. Long-term health outcomes and health system costs associated with surgical site infections: a retrospective cohort study. Ann Surg. 2021;273(5):917-923. doi:10.1097/SLA.0000000000003285
4. Dexter F, Epstein RH, Loftus RW. Quantifying and interpreting inequality of surgical site infections among operating rooms. Can J Anaesth. 2021;68(6):812-824. doi:10.1007/s12630-021-01931-5
5. Wall RT, Datta S, Dexter F, et al. Effectiveness and feasibility of an evidence-based intraoperative infection control program targeting improved basic measures; a post-implementation prospective case-cohort study. J Clin Anesth. 2022;77:110632. doi:10.1016/j.jclinane.2021.110632
6. Dexter F, Parra MC, Brown JR, Loftus RW. Perioperative COVID-19 defense: an evidence-based approach for optimization of infection control and operating room management. Anesth Analg. 2020;131(1):37-42.doi:10.1213/ANE.0000000000004829
7. Dexter F, Elhakim M, Loftus RW, Seering MS, Epstein RH. Strategies for daily operating room management of ambulatory surgery centers following resolution of the acute phase of the COVID-19 pandemic. J Clin Anesth. 2020;64:109854. doi:10.1016/j.jclinane.2020.109854
8. Datta S, Dexter F, Ledolter J, Wall RT, Loftus RW. Sample times for surveillance of S. aureus transmission to monitor effectiveness and provide feedback on intraoperative infection control. Perioper Care Oper Room Manag. 2020;21:100137. doi:10.1016/j.pcorm.2020.100137
9. Robinson ADM, Dexter F, Renkor V, Reddy S, Loftus RW. Operating room PathTrac analysis of current intraoperative Staphylococcus aureus transmission dynamics. Am J Infect Control. 2019;47(10):1240-1247. doi:10.1016/j.ajic.2019.03.028
10. Loftus RW, Dexter F, Robinson ADM. High-risk Staphylococcus aureus transmission in the operating room: a call for widespread improvements in perioperative hand hygiene and patient decolonization practices. Am J Infect Control. 2018;46(10):1134-1141. doi:10.1016/j.ajic.2018.04.211
11. Dexter F, Ledolter J, Epstein RH, Loftus RW. Futility of cluster designs at individual hospitals to study surgical site infections and interventions involving the installation of capital equipment in operating rooms. J Med Syst. 2020;44(4):82. doi:10.1007/s10916-020-01555-0
12. Dexter F, Ledolter J, Epstein RH, Loftus RW. Importance of operating room case scheduling on analyses of observed reductions in surgical site infections from the purchase and installation of capital equipment in operating rooms. Am J Infect Control. 2020;48(5):566-572. doi:10.1016/j.ajic.2019.08.017
13. Dexter F, Ledolter J, Wall RT, Datta S, Loftus RW. Sample sizes for surveillance of S. aureus transmission to monitor effectiveness and provide feedback on intraoperative infection control including for COVID-19. Perioper Care Oper Room Manag. 2020;20:100115. doi:10.1016/j.pcorm.2020.100115