Background: Bacteremia is sometimes observed in patients with prosthetic joint infection (PJI), and it is associated with a lower likelihood of infection control. However, the prevalence and association of bacteremia in chronic PJI remain unknown.
Questions/purposes: (1) What percentage of patients are diagnosed with bacteremia at the time of hospital admission and before surgery for chronic PJI? (2) What clinical factors are associated with positive blood cultures? (3) To what degree are positive blood cultures associated with infection-free implant survival in patients with chronic PJI?
Methods: This prospective study was conducted at a single academic institution from June 2021 to August 2022. Within the study period, we treated 124 patients for chronic PJI, defined according to the modified Musculoskeletal Infection Society (MSIS) criteria. Of those, we considered patients who underwent revision surgery because of chronic PJI of the hip or knee as potentially eligible. All patients received two blood cultures within 48 hours after admission but before surgery. The second blood culture was performed on the contralateral arm 1 hour after the first was completed. Based on that, 87% (108 of 124) of patients were eligible; 13% (16 of 124) were excluded because of delayed blood sample transfers in 6% (7 of 124) of patients, contaminated samples in 2% (2 of 124), late hematogenous infection in 2% (3 of 124), and antibiotic use within 2 weeks before sampling in 3% (4 of 124). No patients were lost before the minimum study follow-up of 2 years without having reached a study endpoint (reinfection or persistent PJI) or had incomplete datasets, leaving 74% (92 of 124) for analysis here. The median (range) time from the index surgery (previous primary, debridement, or revision procedure) to the current revision for PJI in these patients was 16 months (2 to 180). Of the included patients, 40% (37 of 92) were men, 39% (36 of 92) had PJI of the hip, and 61% (56 of 92) had PJI of the knee. The mean age of patients was 65 ± 13 years, and the mean BMI was 28 ± 3 kg/m2. The interval between two cultures was at least 1 hour, and one culture was taken from each of the patient's arms. Patients were divided into blood culture-positive and blood culture-negative groups based on preoperative blood culture results. The chi-square test and the independent t-test were used to compare demographic characteristics (gender, age, BMI, and affected joint) and clinical factors (American Society of Anesthesiologists [ASA] classification, hematological tests, comorbidities) between the two groups. Further multivariable logistic regression analysis was performed to assess the factors associated with positive blood cultures, which controlled for potential confounders including age, gender, BMI, and affected joint. The Firth penalized likelihood was employed when there was monotone likelihood in logistic regression analysis to reduce small-sample bias. A Kaplan-Meier curve tracked infection-free implant survival over 30 months, with differences evaluated using the log-rank test.
Results: Overall, 15% (14 of 92) of patients had positive blood cultures. After adjusting for age, gender, infection site, BMI, and intraoperative isolation of gram-positive cocci, we found that patients classified as ASA III (OR 4 [95% confidence interval (CI) 1 to 21]; p = 0.04) and those who had diabetes (OR 14 [95% CI 3 to 100]; p < 0.001) had a higher odds of positive blood cultures. We found no difference in the Kaplan-Meier estimate for infection-free implant survival at 30 months between those with positive blood cultures (86% [95% CI 76% to 95%]) and those with negative blood cultures (91% [95% CI 88% to 94%]; p = 0.51).
Conclusion: In this prospective, observational study, we found that chronic PJI can potentially lead to hematogenous dissemination of pathogens, particularly in patients with poor overall health (such as those classified as ASA III and patients diagnosed with diabetes). Therefore, selective preoperative blood cultures may be crucial in helping clinicians implement early intervention measures to prevent the serious consequences of bacteremia in patients with poor baseline health and those with other implanted devices. Larger studies with longer follow-up are needed to further validate these findings, ensure more robust estimates, and conduct comprehensive evaluations of the risk factors associated with positive blood cultures in chronic PJI.
Level of evidence: Level II, therapeutic study.
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