A systematic review of distinction of colonization and infection in studies that address Cutibacterium acnes and shoulder surgery.

Abstract

Background: After shoulder surgery, infection is often diagnosed in the absence of an inflammatory host response (purulence, sepsis). In the absence of inflammation, the more appropriate diagnoses may be colonization or contamination. We reviewed the available data regarding culture of Cutibacterium acnes during primary and revision shoulder surgery and asked; 1) what is the prevalence of air, skin, and deep tissue colonization? 2) How often is an inflammatory host response associated with diagnosis of postoperative shoulder infection diagnosed on the basis of culture of C. acnes? 3) Is there any relation between culture of C. acnes and outcomes of shoulder surgery?

Methods: Three databases were searched for studies that address C. acnes and colonization or infection related to shoulder surgery. We analyzed data from 80 studies addressing the rates of C. acnes colonization/infection in patients undergoing shoulder surgery, evidence of an inflammatory host response, and relationship of C. acnes culture to surgery outcomes.

Results: C. acnes is often cultured in the air in the operating room (mean 10%), the skin before preparation (mean 47%), and deep tissue in primary shoulder arthroplasty (mean 29%), arthroscopy (mean 27%), and other shoulder surgery (mean 21%). C. acnes was cultured from a mean of 39% of deep tissue samples during revision arthroplasty. C. acnes was believed to be the causative organism of a high percentage of the infections diagnosed after surgery, 39% in primary shoulder arthroplasties, 53% in revisions, 55% in arthroscopic surgeries, and 44% in a mixture of shoulder surgeries. Infection was nearly always diagnosed in the absence of an inflammatory host response. Documented purulence and sepsis were not specifically ascribed to C. acnes (rather than more virulent organisms such as S. aureus). Diagnosis of infection, or unexpected positive culture, with C. acnes during shoulder surgery is associated with outcomes comparable to shoulders with no bacterial growth.

Conclusions: The evidence to date supports conceptualization of C. acnes as a common commensal (colonization), and perhaps a frequent contaminant, and an uncommon cause of an inflammatory host response (infection). This is supported by the observations that 1) unexpected positive culture for C. acnes is not associated with adverse outcomes after shoulder surgery, and 2) diagnosed infection with C. acnes is associated with outcomes comparable to noninfected revision shoulder arthroplasty. We speculate that diagnosis of C. acnes infection might represent an attempt to account for unexplained discomfort, incapability or stiffness after technically sound shoulder surgery. If so, the hypothesis that stiffness and pain are host responses to C. acnes needs better experimental support.