Table 2

Diagnostic yield of vortexing and sonication fluid culture, depending on two cutoff values (≥1 CFU/ml and ≥50 CFU/ml fluid)a

Cutoff valueNo. (%) of PJI (n = 35)No. (%) of AF (n = 100)% sensitivity (95% CI)% specificity (95% CI)% PPV (95% CI)% NPV (95% CI)% PLR (95% CI)% NLR (95% CI)
Cutoff ≥ 1 CFU/ml
    Sonication fluid25 (71)c7 (7)d71 (54–85)93 (86–97)78 (60–91)90 (83–95)10 (5–21)0 (0–1)
    Vortexing fluid24 (69)8 (8)b69 (51–83)92 (85–96)75 (57–89)89 (82–95)9 (4–17)0 (0–1)
Cutoff ≥50 CFU/ml
    Sonication fluid21 (60)1 (1)e60 (42–76)99 (95–100)95 (77–99)88 (80–93)60 (8–430)0 (0–1)
    Vortexing fluid14 (40)1 (1)e40 (24–58)99 (95–100)93 (68–99)83 (75–89)40 (5–293)1 (0–1)
  • a PJI, prosthetic joint infection; AF, aseptic failure; 95% CI, 95% confidence interval; PPV, positive predictive value; NPV, negative predictive value; PLR, positive likelihood ratio; NLR, negative likelihood ratio.

  • b Propionibacterium acnes (n = 5), coagulase-negative staphylococci (n = 2), Corynebacterium spp. (n = 1).

  • c In 4 of 25 (16%) cases, sonication cultures grew <50 CFU/ml. In all 4 cases, patients had previously received antimicrobial treatment (3 cases were caused by coagulase-negative staphylococci and 1 by Pasteurella multocida).

  • d P. acnes (n = 5), coagulase-negative staphylococci (n = 2).

  • e Corynebacterium spp. (n = 1).