A 20-year-old male presents with fatigue and poor appetite for 5 days, dark urine for 3 days. Physical examination reveals icteric sclera, liver palpable 1 cm below the costal margin, spleen not palpable. ALT is 1250 U/L, anti-HBs (+), anti-HAV IgM (+). He had a history of 'acute icteric hepatitis' 3 years ago, now fully recovered. The most likely diagnosis is: