"This report suggests a widespread outbreak of an undiagnosed respiratory illness in several areas in China as Beijing and Liaoning are almost 800 km apart. It is not at all clear when this outbreak started as it would be unusual for so many children to be affected so quickly. The report does not say that any adults were affected suggesting some exposure at the schools. ProMED awaits more definitive information about the etiology and scope of this concerning illness in China."
Some background on Promed:
https://www.wired.com/story/how-promed-crowdsourced-the-arri...