Age-Related Microbiologic Trends in Periprosthetic Joint Infection of the Knee: Increased Rates of Atypical Pathogens With Increasing Age

Background Periprosthetic joint infection (PJI) after total knee arthroplasty is a morbid complication, particularly in higher complexity patients and atypical infections. There is emerging evidence that age may influence both outcomes and what bacteria are isolated during PJI care. This study sought to identify how microbiological patterns vary across patient age during revision arthroplasty for PJI of the knee. Methods A large database was queried from 2015 to 2023 for adult patients undergoing antibiotic spacer placement for knee PJI. Microbiology data were extracted from synovial and tissue cultures obtained during the hospital admission and grouped into skin flora, enteric, and atypical/hospital-acquired organisms. The change in rates of detecting specific infective organisms by age group (<60, 60-69, 70-79, ≥80) was assessed via linear regression. The microbiological profiles were then compared via chi-squared testing across age groups. Results A total of 6796 patients with microbiological data were identified. PJIs due to skin flora decreased with increasing age (<60: 30.45% vs ≥80: 18.68%, R 2 = 0.903), while enteric pathogens rose with age (<60: 9.91% vs ≥80: 13.75%, R 2 = 0.795). Significantly higher adjusted odds of isolating enteric organisms (adjusted odds ratio=1.35, 95% confidence interval: 1.08-1.69, P = .008) or atypical/hospital-acquired organisms (adjusted odds ratio=1.48, 95% confidence interval: 1.14-1.91, P = .003) were observed in patients ≥80 vs those <80 years. Conclusions Enteric and atypical/hospital-acquired pathogens are more commonly isolated among older adults undergoing surgery for knee PJI. These findings highlight age as an important and understudied factor associated with distinct infective organisms within PJI care.