Project Summary Unprecedented growth has occurred in the use of home-based peritoneal dialysis (PD) in the United States from 30,102 prevalent patients in 2009 to 46,534 patients in 2014, in part due to the new CMS prospective payment system (PPS) for the care of end stage kidney disease (ESKD) patients. PD is considered preferable to facility-based hemodialysis by patients and providers owing to better quality of life, comparable if not superior clinical outcomes, and lower treatment costs. Infection of the PD fluid (peritonitis), affects 15% of US PD patients and is a major complication of PD leading to permanent discontinuation of PD, high rates of hospitalization and death, and increased treatment costs. Preliminary data by our group demonstrating large variation in peritonitis rates across US and international PD facilities suggests that peritonitis is a modifiable healthcare associated infection. Therefore, in an effort to decrease peritonitis rates in the US, we aim to: (1) develop standardized definitions for PD-associated peritonitis, and characterize the variability in PD peritonitis rates, microbiology, and outcomes of peritonitis across US PD facilities to support establishment of a wide- scale national system for peritonitis surveillance; (2) identify patient and PD facility characteristics that affect the risk of peritonitis; (3) identify clinical practices, PD patient training/education program characteristics that affect the risk of peritonitis, and (4) foster the implementation of evidence-based best practice guidelines aimed at preventing peritonitis. We will leverage the existing infrastructure of the Peritoneal Dialysis Outcomes and Practice Patterns Study (PDOPPS), the largest multinational prospective cohort study of PD - capturing extensive patient- and facility- level data on PD treatment practices and outcomes for >6500 PD patients across 182 PD units in 6 countries, including 100 US PD units. The greater variability in PD prevention practices occurring internationally than in the US alone will be advantageous in informing best practices. Key knowledge stakeholders, including representatives from the International Society for PD, the American Society of Nephrology's Nephrologists Transforming Dialysis Safety initiative, the Centers for Disease Control and Prevention, the International Pediatric PD Network, the SCOPE pediatric ESKD collaborative, US dialysis organizations, and PDOPPS will contribute towards our aims of standardizing peritonitis definitions and fostering development of best practice guidelines for preventing peritonitis. Study findings will be a critical step towards implementing evidence-based quality improvement initiatives across PD facilities while fostering future risk-guided peritonitis prevention interventions.