Abstract
Aim
Culture negative (CN) prosthetic joint infections (PJI) account for approximately 10% of all PJIs and present significant challenges for clinicians. We aimed to explore the significance of CN PJI within a large prospective cohort study, and to compare their characteristics and outcomes with culture positive cases.
Methods
The Prosthetic joint Infection in Australia and New Zealand Observational (PIANO) study is a prospective, binational, multicentre observational cohort study conducted at 27 hospitals between July 2014 and December 2017. We compared baseline characteristics and outcomes of all patients with culture negative (CN) prosthetic joint infection (PJI) from the PIANO cohort with culture positive (CP) cases. “Treatment success” was defined as absence of clinical or microbiological signs of infection, no need for ongoing antibiotics, and no need for revision or resection arthroplasty since the end of the initial treatment. We also describe PJI diagnostic criteria in the CN cohort and apply internationally recognised PJI diagnostic guidelines.
Results
Of the 650 patients eligible for inclusion, 55 (8.5%) were CN and 595 were CP. Compared with the CP cohort, CN patients were more likely to be female [32 (58.2%) vs 245 (41.2%); p=0.02], involve the shoulder joint [5 (9.1%) vs. 16 (2.7%); p=0.03] and have a lower mean C-reactive protein (142 mg/L vs. 187 mg/L; p=0.02). Overall, outcomes were superior in CN patients, with culture negativity an independent predictor of treatment success at 24 months (aOR 3.78; 95%CI 1.65 – 8.67). Of the 55 CN cases meeting Infectious Diseases Society of America (IDSA) diagnostic criteria, 45 (82%) met European Bone and Joint Infection Society (EBJIS) criteria (probable or definite) and 39 (71%) met the 2013 Musculoskeletal Infection Society (MSIS) criteria.
Conclusions
Culture negativity is an independent predictor of treatment success in PJI. It is unclear whether this is because some of them are not actually infections, or for other reasons such as lower bacterial load or earlier effective antibiotic treatment. Diagnostic criteria for PJI vary substantially in their sensitivity, with MSIS criteria being the least sensitive.
Acknowledgements
This work is being presented on behalf of the broader PIANO investigators and the Australasian Society for Infectious Diseases Clinical Research Network. The PIANO study received seed funding from Heraeus Medical and the John Hunter Hospital Charitable Trust Fund.
