Which term describes arthritis caused by infection with pathogens documented by culture or nucleic acid amplification test?

• A. Osteoarthritis
• B. Inflammatory Arthritis
• C. Infectious/Septic Arthritis
• D. Crystal Arthropathy

Answer: (C)

Arthritis caused by infection with pathogens documented by culture or nucleic acid amplification test is described as infectious or septic arthritis. The defining feature is direct infectious involvement of the joint with microbiologic proof, so positive culture or NAAT from joint fluid confirms the diagnosis and urgency of treatment. This differs from osteoarthritis, which is degenerative and not infection-driven; inflammatory arthritis, which is immune-mediated without proven infection; and crystal arthropathy, where crystal deposition—not pathogens—drives inflammation. The key takeaway is that microbiologic confirmation within the joint fluid distinguishes septic arthritis from other arthritis types.