Enlarge / Liver lesions in patient with chronic active hepatitis C. (credit: Getty | BSIP)

The cases first came to light in April, when doctors noted an unusual cluster of hepatitis cases in young children in Scotland. The illnesses were not linked to any known cause of hepatitis, such as hepatitis (A to E) viruses, making them unexplained. Though unexplained cases of pediatric hepatitis arise from time to time, a report that month noted 13 cases in Scotland in two months when the country would typically see fewer than four in a year.

Since then, the World Health Organization has tallied more than 1,000 probable cases from 35 countries. Of those cases, 46 required liver transplants, and 22 died. The Centers for Disease Control and Prevention identified 355 cases in the US. As of June 22, 20 US cases required liver transplants, and 11 died.