The World Health Organization has expressed concern over a mysterious strain of severe hepatitis that primarily impacts children. The strain has been identified in 12 countries, with the highest concentration in the United Kingdom, where a child died over the weekend. In 17 of the 169 cases identified worldwide, liver inflammation was so severe the child required a liver transplant. There have been 13 cases found in Spain, 12 in Israel, nine in the U.S. and lower cases in Belgium, Denmark, France, Ireland, Italy, the Netherlands, Norway, and Romania. The WHO says the common cold virus adenovirus could be fueling the wave of acute cases. Of the 169 pediatric cases identified so far, 74 of the children have tested positive for adenovirus.