A 50-year-old man with fatigue, poor appetite, ascites, and jaundice has a history of heroin use. What is the most likely infectious cause of his liver disease?

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The key idea is that intravenous drug use strongly points to a bloodborne viral hepatitis infection, with hepatitis C being the most common infectious cause of chronic liver disease in this group. Hepatitis C virus is transmitted through needle sharing, and many infections become chronic. Over years this chronic inflammation leads to progressive scarring (fibrosis) and eventually cirrhosis. When cirrhosis becomes decompensated, patients can develop fatigue and poor appetite, plus signs like ascites and jaundice as the liver fails to function properly. So, in this clinical picture, hepatitis C is the most likely infectious cause of his liver disease.

Biliary obstruction would cause liver findings related to cholestasis but is not tied to intravenous drug use as a risk factor and isn’t the infectious cause here. Alcohol-related liver disease can cause similar symptoms, but it’s not an infectious cause and the stem’s emphasis on infectious risk (heroin use) makes a viral hepatitis more likely. Pancreatic cancer can cause jaundice by obstructing the bile duct but again is not infectious and doesn’t fit the clue provided by needle-sharing risk.