(CNN) The US Centers for Disease Control and Prevention issued a health advisory to thousands of doctors across the country Thursday, advising them to be on the lookout for a troubling new syndrome that may be associated with Covid-19 infection. The syndrome, called multisystem inflammatory syndrome in children (MIS-C), has been seen in children across Europe and in at least 18 states, plus Washington, DC. Doctors in the UK first alerted other doctors to the syndrome in April. Since then physicians in other countries, including Italy and France, have reported clusters of similar cases. Expect more cases of strange coronavirus syndrome in kids, doctors warn "Beginning about four or five weeks ago, in Europe they stared to describe a form of what really sounded like toxic shock," said Dr. Jeffrey Burns of Children's Hospital and Harvard Medical School in Boston. Burns has been coordinating a series of regular video chats among doctors around the wor