Intra-abdominal infection (IAI) is a major cause of morbidity and mortality in patients with decompensated cirrhosis. However, current diagnostic approaches remain suboptimal. Ascitic fluid culture is time-consuming and often yields low sensitivity, while polymorphonuclear leukocyte (PMN)–based criteria may fail to identify early or clinically equivocal infections, particularly in patients with prior antibiotic exposure or attenuated inflammatory responses. Therefore, there is a critical need for rapid and sensitive adjunctive biomarkers. This study aimed to evaluate the diagnostic utility of ascitic bacterial DNA quantified by droplet digital PCR (ddPCR) for the detection of IAI in cirrhotic patients.

In this multicenter diagnostic study, 623 hospitalized patients with cirrhosis and ascites were consecutively enrolled from six tertiary hospitals. Participants were divided into a development cohort (n=361) and an external validation cohort (n=262). All patients underwent diagnostic paracentesis within 48 hours of admission. Ascitic fluid samples were analyzed using routine laboratory testing, conventional microbiological culture, and 16S rDNA-based ddPCR quantification. IAI was defined using a prespecified composite reference standard, including spontaneous bacterial peritonitis (PMN ≥250 cells/µL) or clinically adjudicated probable infection with PMN <250 cells/µL and compatible clinical features. Diagnostic performance was assessed using receiver operating characteristic (ROC) curve analysis. Subgroup analyses and exploratory serial-sampling assessments were also conducted.

Ascitic bacterial DNA levels were significantly higher in patients with IAI than in those without infection in both cohorts (all P<0.001). In the development cohort, ddPCR demonstrated excellent diagnostic performance with an area under the ROC curve (AUC) of 0.944, and the optimal cutoff value was 458.1 copies/mL. This high level of discrimination was confirmed in the validation cohort (AUC=0.897). Notably, ddPCR retained diagnostic value in patients with PMN <250 cells/µL, indicating its potential role in identifying early or low-grade infections. Among 68 adjudicated IAI cases, ddPCR showed a higher positivity rate than conventional culture (83.8% vs. 67.6%). In addition, ddPCR provided a substantially shorter turnaround time and enabled pathogen detection in some culture-negative cases. Exploratory serial monitoring in a small subset of patients suggested that availability of ddPCR results may facilitate earlier antimicrobial adjustment and reduce short-term antibiotic consumption.

Quantification of ascitic bacterial DNA using ddPCR represents a rapid and sensitive adjunctive diagnostic approach for IAI in patients with cirrhosis. It is particularly valuable in cases with low PMN counts or negative culture results. While preliminary findings suggest a potential role in guiding antimicrobial therapy, further prospective studies are warranted to validate its clinical utility and impact on patient outcomes.