A 55-year-old man presents with abdominal distension and shifting dullness on examination. He has a background of chronic hepatitis C infection. Ultrasound confirms ascites and a nodular liver suggestive of cirrhosis. A diagnostic paracentesis is performed. The ascitic fluid analysis shows: Albumin 15 g/L, WCC 500 cells/mm³ (90% neutrophils). What is the most likely diagnosis?