A 5-year-old boy presenting with limping, right knee pain, and swelling was referred to the orthopedic surgery clinic. He had no known past medical history and had not undergone any surgery or recent dental procedure. The symptoms had been progressing for 3 weeks at the time of presentation. Initial investigation showed normal complete blood count, C-reactive protein (CRP) level, and erythrocyte sedimentation rate (ESR), negative aerobic blood cultures by the VersaTREK system, and a normal knee X-ray. The patient was discharged with a diagnosis of reactive monoarthritis and was given nonsteroidal anti-inflammatory drugs as treatment. A follow-up in a rheumatology clinic was scheduled.
Three weeks later, the patient presented to the emergency room due to a significant progression of the pain, swelling, and limping. Intra-articular effusion was noted on clinical examination. Blood tests showed an elevated CRP level (103 mg/liter) and ESR (59 mm/h). Aerobic blood culture was once again negative. Arthrocentesis of the knee showed a purulent fluid containing 72,000 white cells/μl with 91% neutrophils. Standard aerobic bacterial culture on this fluid was negative. Results for our laboratory-developed bacterial PCR panel, which can detect Staphylococcus aureus, Streptococcus pyogenes, Streptococcus agalactiae, Streptococcus pneumoniae, and Kingella kingae, were also negative. The patient underwent a surgical debridement and irrigation of the joint through a parapatellar arthrotomy. Intravenous cefazolin was started empirically at 150 mg/kg of body weight/day, divided every 8 h (q8h). The articular fluid obtained in the operating room (OR) was once again sent for bacterial culture and multiplex bacterial PCR. The VersaTREK system (Thermo Fisher Scientific) was used to inoculate 1 ml of synovial fluid in a Redox 1 aerobic bottle and a Redox 2 anaerobic bottle in addition to solid medium and enrichment broth (cooked meat). The bacterial PCR result was once again negative. No growth was detected on the solid medium or in the aerobic bottle inoculated with the fluid, but the anaerobic bottle grew the organism shown in Fig. 1 after 15 h of incubation. Solid medium and cooked meat broth were kept for 7 days, and the aerobic bottle inoculated with synovial fluid was kept for 10 days. The antibiotic regimen was then changed to piperacillin-tazobactam at 300 mg/kg/day, divided q6h. Magnetic resonance imaging (MRI) was performed, which showed an important intra-articular effusion, a major thickening of the synovial membrane, and a cartilage lesion on the medial femoral condyle. Two weeks after the introduction of piperacillin-tazobactam, the patient still showed signs of intra-articular inflammation. It was therefore decided he would return to the OR for a second look, which was done arthroscopically. Two weeks after this second look, the patient was still showing signs of inflammation of the knee articulation. It was decided that oral metronidazole would be added to the antibiotic regimen, at 30 mg/kg/day, divided q8h. Given the good clinical course afterwards, the antibiotic regimen was changed 6 weeks after the second look to oral amoxicillin (80 mg/kg/day, divided q8h) for an additional 6 weeks. Eleven months after the initial infection, the patient is doing well, has returned to baseline activities, and has symmetrical range of motion in both knees.
(Left) The bacterium as it appeared on the Gram stain of the anaerobic bottle inoculated with synovial fluid; (top right) MRI of the knee articulation; (bottom right) arthroscopic view of the medial femoral condyle, showing the cartilaginous lesion.
For answer and discussion, see https://doi.org/10.1128/JCM.01294-17 in this issue.
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