Cultures
Strong evidence supports that synovial fluid and tissue cultures are strong rule-in tests for the diagnosis of infection; negative synovial fluid and tissue cultures do not reliably exclude infection.

Rationale
RATIONALE
Ten high quality studies were identified that addressed the role of culture in the diagnosis of surgical site infection; notably only two of the studies (Holinka, Puig-Verdie) included patients with infections involving orthopaedic sites other than hip or knee arthroplasties.

SYNOVIAL FLUID CULTURES
Three high quality studies (Gallo, Tomas, Spangehl) evaluated the yield of synovial fluid cultures in the diagnosis of prosthetic joint infection. Two of the studies found strong evidence to support fluid culture in the diagnosis of PJI (Tomas, Spangehl) while one found moderate evidence in support (Gallo).

INTRAOPERATIVE TISSUE CULTURES
Seven high quality studies evaluated the yield of intra-operative tissue cultures in the diagnosis of surgical site infection (Aggarwal, Holinka, Hughes, Panousis, Puig-Verdie, Spangehl, Trampuz). Of these, six of the seven studies revealed strong evidence in support of tissue culture to rule in the diagnosis of infection; one found the evidence to be moderate (Holinka). Additionally, the method by which the organism was grown was relevant. In these seven studies, there was variability in the performance of tissue culture in excluding infection. One high quality study evaluated the value of positive culture only from enrichment broth (Smith). Broth-only positive cultures showed poor correlation as a rule-in or rule-out test for infection. Two high-quality studies evaluated the performance of tissue cultures compared with swab cultures (Aggarwal, Spangehl). Both demonstrated better accuracy of tissue cultures over swab cultures.

NUMBER OF INTRAOPERATIVE CULTURES
Multiple tissue cultures should be collected to improve the accuracy of infection diagnosis. One moderate quality study (Atkins) quantified the number of samples needed to confirm the diagnosis of infection. A single positive culture for an organism of limited virulence was shown to have poor predictive value as a rule-in test. Two distinct positive cultures for the same organism provided strong evidence of periprosthetic infection.

DURATION OF CULTURE INCUBATION
One high quality (Schafer) and one moderate quality (Butler-Wu) study reviewed the duration of culture incubation for chronic periprosthetic infection. Both studies demonstrated improved yield when both aerobic and anaerobic cultures were incubated for 14 days.

PRIOR ANTIBIOTIC EXPOSURE
One high quality study evaluated the effect of prior antibiotic therapy on the yield of sonicate and tissue culture. The yield of culture was reduced when antibiotic therapy was administered within 14 days of culture collection.
 

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