The Utility of Acid-Fast Bacillus (AFB) and Fungal Cultures in Orthopaedic Infections.

Introduction When diagnosing suspected orthopaedic-related infections, fungal and acid-fast bacilli (AFB) cultures are often obtained intraoperatively. These cultures are difficult and time-consuming to grow and increase healthcare costs. This study aimed to quantify the rate of positive AFB and fungal cultures in orthopaedic infections and to compare potential risk factors for a positive result.  Methods Orthopaedic surgical cases for suspected infection at one institution from March 2013 through December 2019 were included. Data were collected on patient demographics and procedure characteristics for patients with surgical AFB or fungal lab tests ordered on the day of surgery. Results Of the 813 patients for whom intraoperative AFB or fungal cultures were ordered, 3.8% (N=31) had a positive result. Of the 31 positive results, 30 were from fungal cultures and one was from AFB cultures. Patients with a positive versus negative culture result did not differ significantly by age, sex, American Society of Anesthesiologists (ASA) score, diabetes, obesity, or HIV/AIDS. In both unadjusted and adjusted analyses, peripheral vascular disease (PVD) was associated with higher odds of a positive fungal culture result (adjusted OR (aOR)=3.5, 95%CI=1.3-8.4). Likewise, in both unadjusted and adjusted models, a hand/foot operating region was associated with higher odds of a positive fungal culture result compared with all other regions (aOR=4.2, 95%CI=1.9-9.8). Conclusion Intraoperative fungal and AFB cultures may not need to be obtained except in orthopaedic surgical cases for hand or foot infections or in patients with PVD.