Study data presented at the AAOS Annual Meeting indicate that a minimum of five periprosthetic samples need to be cultured and held for at least 14 days to reach a diagnosis of periprosthetic joint infection (PJI) following total joint arthroplasty (TJA). 

“The lack of robust evidence for the optimal number and incubation duration of culture samples needed to reach a definitive diagnosis of PJI prompted us to conduct the study,” explained coauthor Michael Maher Kheir, MD. “Current recommendations state that three to five distinct intraoperative tissue samples be collected for aerobic and anaerobic cultures and maintained anywhere from 3 to 14 days. When less virulent organisms are suspected, collection of up to 10 periprosthetic samples has even been proposed. Our goal was to provide evidence-based recommendations for the minimum number of samples and growth duration required to reach a diagnosis of PJI based on an analysis of 2,290 culture samples at our institution.” Organism type vs. number of days/samples.
Courtesy of Michael Maher Kheir, MD Retrospective review of prospectively collected data
The 2,290 culture samples had been obtained from 711 TJA patients (329 hips, 382 knees) and sent for analysis between 2000 and 2014. Only PJIs that met the Musculoskeletal Infection Society (MSIS) criteria for infection and had available culture results were included in the study; PJIs with polymicrobial organisms were excluded. Culture results for the samples were obtained from electronic medical records and assessed for culture positivity, the identity of the organism growing, antibiotic susceptibilities, number of cultures per PJI case, type of culture, and the number of culture incubation days until growth was identified. Mean culture growth duration for positive cultures was calculated and stratified by the following organism types: antibiotic-resistant, Staphylococcus aureus, gram-positive organisms, coagulase negative Staphylococcus spp (CNS), gram-negative organisms, atypical organisms, Proprionibacterium acnes (P acnes), and Escherichia coli. The number of culture samples needed for each organism was calculated per MSIS recommendations and Infectious Diseases Society of America guidelines. Results
Statistical analysis revealed that the average number of samples needed to get two positive cultures based on percentage positivity was 4 (62.6 percent, 1433/2290), and that the percentage of positive cultures varied by organism (P < 0.001).  “We found that all organisms could be detected with five or fewer culture samples. The exceptions include atypical organisms and P acnes, which represented 5 percent of all PJIs,” said Dr. Kheir (Table 1). “Although the majority of organisms were cultured in 5 days or less, 10.8 days were required for P acnes, 6.6 days for atypical organisms, and 5.2 days for CNS,” he added. “Given that the organism is likely unknown at the time of surgery in many cases, we recommend obtaining at least five periprosthetic samples and holding cultures for at least 14 days for the diagnosis of PJI,” said Dr. Kheir. “Organism virulence plays an influential role on the minimal number of cultures and the duration of incubation needed. In cases of culture-negative PJI, or when there is suspicion for low virulent organisms, the duration of the culture and number of samples may need to be increased.”               

Dr. Kheir's coauthors of “Determining the Number and Duration of Cultures for Diagnosing Periprosthetic Joint Infection” are Timothy L. Tan, MD; Colin Thomas Ackerman, BS; Ronuk Modi, BS; Dean D. Tan, BS; and Javad Parvizi, MD.

Details of the authors' disclosure as submitted to the Orthopaedic Disclosure Program can be found in the Final Program; the most current disclosure information may be accessed electronically at www.aaos.org/disclosure Maureen Leahy is assistant managing editor of AAOS Now. She can be reached at leahy@aaos.org

Bottom Line

• Little evidence exists regarding the optimal number and incubation duration of culture samples needed to reach a definitive diagnosis of PJI following TJA.
• This study analyzed 2,291 culture samples from TJA patients to determine the minimum number of samples and growth duration required to reach a diagnosis of PJI.
• The researchers found that all organisms could be detected with five or fewer culture samples. They recommend obtaining at least five periprosthetic samples and holding cultures for at least 14 days for the diagnosis of PJI.