It wasn’t just that people were getting sick—it was who. And how many. Hepatitis A is a viral disease that primarily attacks the liver, and if it gets serious—as it can in the elderly and immune-compromised people—it can be fatal. But the graph of cases in the US over time looks like the second, fun half of a roller coaster ride. In the early 1970s, nearly 10,000 people a year got it. By the mid-1980s, the number was half that.