A patient has a draining sinus at the site of a left total hip arthroplasty.

Theoptimal specimen for identifying the etiologic agentin a prosthetic joint infection (PJI) is ajoint aspirate(synovial fluid). This is because:

It provides direct access to the infected sitewithout contamination from external sources.

It allows for accurate microbiologic culture, Gram stain, and leukocyte count analysis.

Why the Other Options Are Incorrect?

A. Blood– Blood cultures may help detecthematogenous spreadbut are not the best sample for identifyinglocalizedprosthetic joint infections.

B. Wound drainage– Wound cultures oftencontain contaminantsfrom surrounding skin flora and do not accurately reflect joint space infection.

D. Sinus tract tissue– Cultures from sinus tracts often representcolonization rather than the primary infecting organism.

CBIC Infection Control Reference

APIC guidelines confirm thatjoint aspirate is the most reliable specimen for diagnosing prosthetic joint infections​.