Time-dependent microbiology of peripancreatic drainage fluid in severe acute pancreatitis: a prospective real-world observational study using metagenomic sequencing and culture.

Objective: The microbiological characteristics of peripancreatic collections in severe acute pancreatitis (SAP) evolve over time, yet prospective data linking pathogen detection to disease timing and first intervention remain limited. Methods: This prospective single-center observational study enrolled 20 patients with SAP undergoing first-time percutaneous catheter drainage (PCD) for suspected infected pancreatic necrosis (IPN). Peripancreatic drainage fluid samples were simultaneously analyzed by conventional microbiological culture and metagenomic next-generation sequencing (mNGS). Microbiological positivity rates were compared according to time from disease onset (≤14 vs. >14 days). Results: Overall, mNGS was positive in 9/20 cases (45.0%) and conventional culture in 6/20 cases (30.0%). When stratified by time from disease onset, microbiological positivity was low within 14 days (mNGS: 1/7, 14.3%; culture: 1/7, 14.3%), but increased in patients undergoing drainage beyond 14 days (mNGS: 8/13, 61.5%; culture: 5/13, 38.5%). mNGS identified a broader spectrum of pathogens, particularly polymicrobial, anaerobic, and fungal organisms. Conclusion: In this prospective observational cohort, peripancreatic collections were predominantly culture- and mNGS-negative during the early phase of SAP, supporting the concept that early necrosis is commonly sterile. In later stages, mNGS provides complementary microbiological information beyond conventional culture. These findings offer descriptive real-world evidence on the time-dependent microbiology of suspected IPN and may inform future studies on optimized diagnostic and antimicrobial strategies.