Septic arthritis in a native joint due to Anaerococcus prevotii

Area of Science:

• Infectious Diseases
• Microbiology
• Rheumatology

Background:

• Septic arthritis is a serious joint infection often caused by Staphylococcus aureus.
• Injecting drug use is a significant risk factor for developing septic arthritis.
• Standard antibiotic treatments may not be effective against less common pathogens.

Observation:

• A 37-year-old male injecting drug user presented with symptoms of septic arthritis.
• Initial blood cultures grew Staphylococcus aureus, but treatment with flucloxacillin and fusidic acid was ineffective.
• Knee aspirate culture, after a prolonged incubation period, identified Anaerococcus prevotii.

Findings:

• Anaerococcus prevotii was the causative agent of septic arthritis in this case.
• A large thigh abscess containing Anaerococcus prevotii was drained.
• The patient's condition improved significantly after the addition of metronidazole to the treatment regimen.

Implications:

• This case underscores the importance of considering rare anaerobic bacteria, such as Anaerococcus prevotii, in the differential diagnosis of septic arthritis, especially in high-risk individuals.
• Extended incubation times for cultures may be necessary for identifying fastidious organisms.
• Successful treatment involved a combination of surgical drainage, appropriate antibiotics (including metronidazole), and addressing the underlying risk factor (drug use).