The Incidence and Incubation Period of False Positive Cultures in Shoulder Surgery

Postoperative infection is a significant complication that requires timely identification and treatment. Indolent infections, such as those involving Propionibacterium acnes (P. acnes), pose a diagnostic dilemma as they present differently than the acute symptoms typically associated with most postoperative bone and joint infections. The workup of these suspected infections is also somewhat difficult, as these colonies are slow growing, necessitating that cultures be kept for an extended period of time. Previous studies have shown that positive cultures are typically identified between 7 and 13 days. In a recent study of patients undergoing primary shoulder arthroplasty, 41.8% of patients were found to have P. acnes growth from their joint fluid at a mean of 7 days (range 5-9 days). All of these patients were then treated immediately with 4 weeks of dual oral antibiotic therapy1.

As the incubation of laboratory cultures increases, there is the potential concern of false positive growth. Timely identification is critical in order to avoid performing unnecessary treatments on patients in whom no infection is actually present.

The investigators will enroll patients undergoing primary shoulder surgery for a clearly identified mechanical dysfunction, in which there is no clinical suspicion for infection. Infection should not exist in this population, making it an appropriate clinical sample in which to study results that the investigators would consider to be false positives.

Inclusion criteria

• Patients undergoing primary open and arthroscopic shoulder surgery in which there is a clear diagnosis of a mechanical problem that is felt to be amenable to surgical intervention and there is no suspicion of infection. Examples include, but are not limited to: rotator cuff tear, labral tear, instability, impingement, and osteoarthritis.

Exclusion criteria

• Prior shoulder surgery
• Prior glenohumeral injection within the last 6 months
• Systemic or shoulder inflammatory disorder
• Any clinical, imaging, or laboratory findings that raise suspicion of infection
• Minors
• Erythrocyte sedimentation rate (ESR) >15 mm/hr for males less than 50 years old, >20 mm/hr for males greater than 50 years old and females less than 50 years old, and >30 mm/hr for females greater than 50 years old
• C reactive protein (CRP) >1 mg/d,
• Procalcitonin (PCT) >0.05 ng/ml.