Acute Bacterial Arthritis: How Long Should You Wait for Culture Results?
Methods: We reviewed the charts of 94 adults who had monoarthritis less than two weeks prior to admission. Patients with disseminated gonococcal disease and the results of repeat synovial fluid cultures from the same admission were excluded. Subjects with at least one of the following were considered high-risk: ≥ 80 years old, rheumatoid arthritis, diabetes mellitus, malignancy, chemotherapy or immunosuppressant therapy, joint prosthesis in the affected joint, peripheral leukopenia, human immunodeficiency virus infection, and a history of crystal-induced arthropathy. The positivity rate and time to positivity of synovial fluid in combined agar plate and broth culture were calculated.
Results: The overall positivity rate was 22.3% (21 of 94). None of the 21 low-risk patients had a positive culture result. Twenty one of 73 (28.7%) high-risk subjects showed growth, with a mean time to positivity of 36.7 ± 27.1 hours. While half of these turned positive within a day of incubation, growth was detected up to 90 hours. The positivity rates did not differ significantly (P=0.23) between those who received antibiotics prior to arthrocentesis (8 of 26, 30.8%) and those who did not (13 of 68, 19.1%). There was also no significant difference (P=0.90) in the rates between those who had crystals detected in the synovial fluid (6 of 26, 23.1%) and those who had none (14 of 64, 21.9%). Diabetic subjects were more likely (P=0.0001) to have a positive culture result than nondiabetic subjects (RR=7.4). Four of seven patients with an HIV infection grew bacteria from their synovial fluid, three of which were MRSA.
Conclusion: In patients with acute monoarthritis, waiting for culture results until the fourth day of incubation, and maybe even later, is reasonable. This is especially true for high-risk patients. The presence of crystals in itself, even in the absence of bacterial growth after 24 hours, should not trigger the discontinuation of antibiotic treatment.
S. Pomerantz, None