Forty years ago, a beloved neighbor was bedridden for weeks at a time with a mysterious ailment. She knew only that it involved her liver and that she must never drink alcohol, which would make things worse.

It was decades before the cause of these debilitating flare-ups was discovered: a viral infection at first called non-A, non-B hepatitis, then properly identified in 1989 as hepatitis C. The apparent source of her infection was a blood transfusion she had received decades earlier.

read more at the New York Times