What are the most common organisms causing prosthetic joint infection?
Early infections (<3 months post total joint arthroplasty) are caused by S. aureus, Streptococcus, or Gram-negative bacilli. Usually due to surgical contamination. These patients present with fever and local signs of wound infection typical of septic arthritis.
Delayed infections (3–24 months) are usually caused by indolent organisms such as coagulase-negative Staphylococci ( S. epidermidis ) or C. acnes . These organisms can get in the polysaccharide mucoid biofilm (glycocalyx) that forms on the prosthetic joint and provides a protective environment for bacterial growth. Patients present with progressive joint pain but frequently do not have other symptoms typical of septic arthritis. Fever occurs in <50% and leukocytosis in 10%. Elevated ESR and CRP are common.
Late infections (>24 months) are due to hematogenous seeding from a distant site of infection such as skin, mouth, or urinary tract. Patients have acute onset of joint pain, swelling, and fever typical of septic arthritis.
Pearl: C. acnes often takes 7-10 days to grow (ask the microbiology lab to hold the plates).