Understanding the Utility of Automation for Diagnosing Spontaneous Bacterial Peritonitis and Its Variants

Spontaneous bacterial peritonitis (SBP) is the most frequent bacterial infection in cirrhotic patients with ascites, marking early hepatic decompensation. Variants of SBP are classified based on ascitic fluid polymorphonuclear neutrophil count and culture positivity.

A prospective cross-sectional study was conducted from 2014 to 2016 at a tertiary care hospital in South India. The study compared the diagnostic yield of conventional versus automated culture methods for detecting SBP and its variants. Ascitic fluid samples were cultured using conventional culture and/or automated culture methods, based on the clinician's preference.

Among 190 patients with ascites, automated culture was performed in 175 patients (92%) and conventional in 82 patients (43%). An automated blood culture system detected pathogens in 70 patients (40%), whereas conventional methods were positive in only eight cases (9.8%). After excluding contaminants, the overall culture positivity was seen in 45 patients (23.1%). Escherichia coli was the most frequently isolated pathogen. Notably, rare organisms such as Campylobacter spp., Aeromonas spp., Beta-hemolytic streptococci, and Salmonella typhimurium were isolated exclusively via automated culture. Accordingly, patients were also categorized into SBP (24 patients; 13%), culture-negative neutrocytic ascites (CNNA) (17 patients; 9.2%), and monobacterial bacterascites (MNB) (18 patients; 9.7%).

Automated culture systems significantly outperform conventional methods in detecting bacterial pathogens in ascitic fluid, with a fourfold higher detection rate. Their ability to isolate fastidious organisms underscores their utility as the preferred first-line diagnostic tool in suspected SBP.