When previously healthy little kids started showing up in hospitals with failing livers last fall and this spring, startled doctors and public health authorities didn’t know what was behind what they were seeing. They also didn’t know if what they were seeing was new.
There have always been cases of hepatitis in children for which a cause cannot be found — such cases are labeled pediatric hepatitis of unknown etiology. But these cases occur in very low numbers and they aren’t well studied or tracked. So when doctors in Alabama and Scotland reported seeing more of these cases over a few weeks then they would normally see in a year, they didn’t have reliable statistics against which to compare the seeming surge.