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Culture negative PJI periprosthetic joint infection: Strategies to improve yield
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Cultures of tissue or fluid obtained from an affected joint constitute an important component of the diagnosis and treatment of periprosthetic joint infection.
According to its new definition, the sole isolation of a pathogen by culture from two separate tissue or fluid samples that are obtained from the affected prosthetic joint are used to diagnose a periprosthetic joint infection (PJI). Additionally, when a pathogen is identified, the antibiotic treatment can be tailored using specific sensitivity. Unfortunately, in 7% to 12% of PJI cases, cultures may be negative even in the presence of clear signs of infection. It is also important to note that cultures are used to confirm and not to screen for PJI.
Negative cultures may be caused due to various reasons, including the use of antimicrobial therapy prior to the collection of fluid or tissue, inappropriate collection of tissue samples (i.e., excessive cauterization) and the use of short periods of incubation, especially when low virulence pathogens cause the infection. Some pathogens are difficult to identify using traditional tissue cultures, particularly if they are encapsulated in biofilm, or when fungi or mycobacteria are the culprits and a specific medium culture for these pathogens is not used. Negative cultures limit the tailoring of the antibiotic treatment and, moreover, hinder the justification for revision surgery if other components of the PJI definition are not present. Lack of identification of the infecting organism also poses challenge regarding the selection of appropriate antibiotics for addition to the cement spacer and also in the postoperative period. In order to cover all possible infecting organisms, often a broad spectrum antibiotic or multiple antibiotics are administered that place the patient at systemic risk and carry the disadvantage of not treating fungi and rare organisms.
The most effective strategy to improve the culture yield is to withhold aspiration of the joint for at least 2 weeks after the last dose of antibiotic. The latter is based on the available evidence evaluated by the work group that was convened by the American Academy of Orthopaedic Surgeons. The other recommendation of the same work group was to withhold administration of antibiotic to any patient with suspected PJI until appropriate tests, such as joint aspiration, for diagnosis of PJI are performed.
 Javad Parvizi |
 Carlos Higuera |
Another strategy to improve yield of culture is to prolong the period of incubation of culture samples for at least 14 days and possibly 21 days. The tissue or fluid samples obtained from the joint should also be transferred to the laboratory for immediate processing in all cases, in general, and in culture negative cases in particular. It is our practice to call the microbiology department and inform them of the challenge of isolating the infecting organism and “warn” them about the sample being sent. The appropriate use of culture media is paramount to obtain accurate positive cultures. If fungi or mycobacteria infection is suspected, the proper media should be used. Cultivation of samples should be performed under sterile conditions, ideally using a laminar flow workbench. Some authorities also propose the use of enriched medium for all cultures, such as trypticase-soy agar containing sheep blood, chocolate agar, MacConkey agar and brain-heart infusion broth.
Another reason for false negative PJI cases relates to aggregation of the infecting organism in a biofilm. In the biofilm, the organisms are able to communicate through sophisticated molecular mechanisms, such as quorum sensing, and avoid destruction by the host’s immune system.
Biofilm disruption techniques to “mobilize” the infecting organism have been described. Sonication of the retrieved prosthesis is one such method that is reported to improve yield of culture. However, not all centers are equipped to perform sonication of the retrieved prostheses limiting the use of this technique. The advantages of this technique include the fact that it is simple, reproducible and it yields viable microorganisms that can be subjected to antimicrobial susceptibility testing. The sonication fluid also typically yields a high number of organisms, which may help to distinguish between infected and contaminated prostheses.
Role of molecular techniques
The introduction of molecular techniques offers another option when negative cultures are present in patients where PJI is suspected. Polymerase chain reaction (PCR)-based assays increase the sensitivity of cultures. There are multiple PCR-based techniques using either species-specific primers or broad-range primer pair to 16S rRNA gene to amplify DNA. However, these techniques carry extreme sensitivity, leading to a higher incidence of false positive cultures. We have been evaluating the role of multiplex PCR (Ibis T5,000) that relies on pan-genomic amplification, and mass spectrometry for culture negative cases. The results, so far, have been encouraging. Following amplification process and isolation of the organism, fluorescent in situ hybridization (FISH) has also been used to confirm that the organisms were indeed real and not contaminants.
Other alternatives for improving high false-positive results include the use of ribosomal RNA-based PCR, which has shown a specificity close to 100% and a sensitivity equivalent to intraoperative cultures. This technique retains the cell viability-sensitive degradation patterns of RNA even after 7 days of sterilization, while retaining the ability to identify infections. This technology is still in the process of becoming fully available in the clinical practice.
The slow transition of molecular techniques into clinical applications has shown promising results. A progressive decrease in cost and increase in the availability of this technology may provide the clinician with another tool to enhance the identification of pathogens in patients with high suspicion of having PJI, where a confirmation of the diagnosis would guide the appropriate treatment and improve outcomes. Further research with large, multicenter cohorts is needed to understand the practicality of these techniques.
In the presence of negative cultures in patients with high suspicion of PJI, it is paramount to understand its potential causes, and to expand the type and incubation period of the cultures in order to rule out infection with low virulence pathogens, fungi or mycobacteria.
References:
- Berbari EF, Marculescu C, Sia I, et al. Culture-negative prosthetic joint infection. Clin Infect Dis. 2007;45:1113-1119.
- Bergin PF, Doppelt JD, Hamilton WG, et al. Detection of periprosthetic infections with use of ribosomal RNA-based polymerase chain reaction. J Bone Joint Surg Am. 2010;92(3):654-663.
- Della Valle C, Parvizi J, Bauer TW, et al. Diagnosis of periprosthetic joint infections of the hip and knee. J Am Acad Orthop Surg. 2010;18(12):760-770.
- Parvizi J, Ghanem E, Menashe S, et al. Periprosthetic infection: What are the diagnostic challenges? J Bone Joint Surg Am. 2006;88 (4):138-147.
- Parvizi J, Zmistowski B, Berbari EF, et al. New definition for periprosthetic joint infection: From the Workgroup of the Musculoskeletal Infection Society. Clin Orthop Relat Res. 2011;469:2992-2994.
- Javad Parvizi, MD, FRCS, editor of Infection Watch, can be reached at the Rothman Institute, 925 Chestnut St., 5th Floor, Philadelphia, PA 19107; 267-339-3617; email: parvj@aol.com.
- Carlos A. Higuera, MD, can be reached at carhiguera75@yahoo.com.
- Disclosures: Parvizi is a consultant to Stryker. Higuera has no relevant financial disclosures.