CORRInsights®: False-positive Cultures After Native Knee Aspiration: True or False

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Excerpt

Clinicians often debate the best ways to confirm a joint infection. The consequences of a delayed or missed infection diagnosis are substantial. Timeliness of diagnosis in patients with prosthetic knee joints may be the difference between treatment with a single operation and a staged revision, or on rare occasions, an above-the-knee amputation [2]. In an attempt to clarify the diagnostic process, the Musculoskeletal Infection Society recently developed a consensus statement [3] addressing the definition and diagnosis of a periprosthetic joint infection (PJI). The criteria to confirm a joint infection include: Two positive cultures (on two separate samples) are a major criteria and one positive culture qualifies as a minor criteria. Other minor criteria include ESR and CRP blood tests.
The current study by Jennings and colleagues also brings us one step closer to appropriately interpreting culture data in patients without arthroplasties in whom the diagnosis of pyarthrosis is being entertained. The authors contend that prior to their study, culture reports of nonvirulent organisms such as normal skin flora were often dismissed as false-positive results. Though the consequences can vary, a delay in diagnosis and treatment of a native joint infection could lead to preventable joint destruction.
Jennings and colleagues set out to study false-positive culture results by aspirating a series of knees with no clinical signs of infection using needles containing stylets to minimize the risk of harvesting skin plugs, which could contaminate knee aspiration resulting in false positive culture results [6]. They took extensive steps to minimize the risk of inadvertent contamination that has been observed in other studies on the topic [1, 8, 9, 11]. Specifically, they performed the experiment in the operating room, with a full surgical skin preparation, body-exhaust suits, and sterile technique. This laborious process gives credence to their findings of no false-positive cultures.
To some degree, the diagnosis of infection has been made easier in recent years. Alpha-defensin testing [4, 5, 7, 10] offers a high degree of sensitivity and specificity. Although this test currently does not provide immediate results, a same-day process currently is available in Europe (and is making its way through regulatory channels in the United States). Even so, for purposes of tailoring antimicrobial therapy, accurate cultures are critical and are likely to remain so for the foreseeable future, so the work of Jennings and colleagues is quite important.
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