A 42-year-old male with cirrhosis and ascites presents with fever (temperature ~38.5°C) for 3 days, abdominal pain, and increased ascites. Ascitic fluid analysis shows: pale yellow appearance, specific gravity 1.017, protein 25g/L, total cell count 0.6×10<sup>9</sup>/L (600/mm<sup>3</sup>), WBC 0.4×10<sup>9</sup>/L (400/mm<sup>3</sup>), neutrophils 80%. The most likely complication is: