The World Health Organization reported that 650 children have been diagnosed with cases of severe hepatitis across 33 countries since the beginning of April. The disease, the WHO said, now represents a “moderate” global health risk. Of the 650 cases, 38 children have required liver transplants and nine have died. More than half the cases have come from Europe. Adenovirus, a common pathogen found in children, has been detected in more than half of the recent cases, but the cause of the severe acute hepatitis is still unknown and under investigation. The WHO said in a statement that adenovirus does not fully explain the increased severity of the cases. The WHO described the cases as “more clinically severe” and more likely to lead to “acute liver failure” than prior reports of hepatitis in children.