Descriptive Epidemiology of Invasive S. aureus (SA) Infections Following Orthopedic Procedures

Background:   As surgical techniques improve and the population ages, the volume of orthopedic procedures being performed will increase. SA infection has been noted as a complication following orthopedic surgery.  Understanding the epidemiology of invasive SA infections following various orthopedic surgeries is important to quantify the burden of this serious complication.

Objective: To describe the epidemiology of invasive SA infections following orthopedic procedures

Methods: Prospective cohort of 50,378 adults undergoing ≥ 1 orthopedic procedures with clean and clean-contaminated wound class at 11 hospitals (9 community and 2 tertiary-care hospitals) from 2003-2006.   “Invasive infection” was defined as the presence of a deep/organ space surgical site infection (SSI) within 30 days (for non-implant procedures) or 1 year (for implant procedures) following surgery or a bloodstream infection (BSI) within 90 days following surgery.  Incidence rates were estimated and nonparametric bootstrapping was used to generate 95% confidence intervals (CIs).  Generalized estimating equations regression was performed to assess the association between SA infection and procedure while controlling for risk index variables (ASA score, wound class, and procedure time), hospital type, and patient age.

Results:  A total of 174 invasive SA infections were identified during the study period.  The overall rate for invasive SA infection was 0.35/100 procedures (95% CI 0.30-0.40); for SA SSI was 0.26/100 procedures (95% CI 0.22-0.31), and for SA BSI was 0.12/100 procedures (95% CI 0.09-0.15).  The median time to infection was 23 days. Over half of the infections were methicillin resistant (MRSA). Rates of infection, median time to infection, and percentage of MRSA by procedure type are summarized in Table 1. The highest rate of invasive SA infection was found following amputation (AMP), predominantly due to BSI.  The majority of infections following insertion of knee (KPRO) or hip (HPRO) protheses were SSI.  More than 90% of the SSI following KPRO and HPRO were captured within the first 120 days following surgery.  The odds of patients developing invasive SA infection following either AMP (odds ratio (OR): 11.9; 95%CI: 5.0-28.3), KPRO (OR: 3.7; 95% CI: 2.0-6.9), HPRO (OR: 4.9; 95% CI: 3.1-7.7) or open reduction and internal fixation of a fracture (FX) (OR: 2.6; 95%CI: 1.7-4.1) were significantly greater than those of patients undergoing other musculoskeletal procedures (OMS).

Conclusions:   Rates of postoperative invasive SA infections were found to vary between different orthopedic procedure types.  Patients undergoing amputations, insertion of knee or hip prostheses, and open reduction and internal fixation of a fracture are at significant risk for invasive SA infection.  Due to morbidity and mortality associated with invasive SA infections, novel strategies to prevent and treat these infections are warranted.