Forty-two participants (54%) had Staphylococcus aureus and 31 participants (40%) had coagulase-negative staphylococci infections, while 11 gram-negative organisms (14%) and 6 gram-positive anaerobic cocci (8%) infections were noted. Cutibacterium acnes and Streptococcus agalactiae were each found in 3 participants (4% of), and diphtheroids (not further identified) was found on 2 participants (3%). Candida albicans was identified in a single participant (1%), along with coagulase-negative staphylococci, and 2 participants (3%) had no identified organisms. There were multiple organisms isolated from 20 patients (26%).
Fifty participants had clear documentation in their EHR that cure of infection was the goal, meeting the criteria for the intent-to-cure group. The remaining 28 participants were placed in the without-intent-to-cure group. Success and failure rates were only measured in the intent-to-cure group, as by definition the without-intent-to-cure group patients would meet the criteria for failure (removal of prosthesis or long-term antibiotic use). The without-intent-to-cure group had a higher median age than the intent-to-cure group (69 years vs 64 years, P = .24) and a higher proportion of male participants (96% vs 80%, P = .09). The median (IQR) implant age of 11 months (1.0-50.5) in the without-intent-to-cure group was also higher than the median implant age of 1 month (0.6-22.0) in the primary group (P = .22). In the without-intent-to-cure group, 19 participants (68%) had a chronic infection, compared with 11 (22%) in the intent-to-cure group (P < .001).
The mean (SD) Charlson Comorbidity Index in the without-intent-to-cure group was 2.5 (1.3) compared with 1.9 (1.4) in the intent-to-cure group (P = .09). There was no significant difference in the type of implant or microbiology of the infecting organism between the 2 groups, although it should be noted that in the intent-to-cure group, 48 patients (96%) had Staphylococcus aureus or coagulase-negative staphylococci isolated.
The median (IQR) dosage of rifampin was 600 mg (300-900). The secondary oral antibiotics used most often were 36 fluoroquinolones (46%) followed by 20 tetracyclines (26%), 6 cephalosporins (8%), and 6 penicillins (8%). Additionally, 6 participants (8%) received IV vancomycin, and 1 participant (1%) was given an oral antifungal in addition to a fluoroquinolone because cultures revealed bacterial and fungal growth. The median (IQR) duration of antimicrobial therapy was 3 months (1.4-3.0). The mean (SD) duration of antimicrobial therapy was 3.6 (2.4) months for TKA infections and 2.4 (0.9) months for THA infections.
Clinical Outcome
Forty-one intent-to-cure group participants (82%) experienced treatment success. We further subdivided the intent-to-cure group by implant age. Participants whose implant was < 2 months old had a success rate of 93%, whereas patients whose implant was older had a success rate of 65% (P = .02).
Secondary Outcomes
The median (IQR) duration of antimicrobial treatment was 3 months (1.4-3.0) for the 38 patients with TKA-related infections and 3 months (1.4-6.0) for the 29 patients with THA infections. AEs were recorded in 24 (31%) of all study participants. Of those with AEs, the average number reported per patient was 1.6. Diarrhea, gastric upset, and nausea were each reported 7 times, accounting for 87% of all recorded AEs. Five participants reported having a rash while on antibiotics, and 2 experienced dysgeusia. One participant reported developing a yeast infection and another experienced vaginitis.