More than a dozen children have fallen ill with a new and potentially fatal combination of symptoms apparently linked to Covid-19, including a sore stomach and heart problems. The children affected appear to have been struck by a form of toxic shock syndrome. All have been left so seriously unwell that they have had to be treated in intensive care. At least one has received extra corporeal membrane oxygenation (ECMO) treatment, which is used when someone’s life is at risk because they can no longer breathe for themselves. NHS bosses are so concerned that they have written to doctors alerting them to the emergence of these cases and asked them to urgently refer any children with similar symptoms to hospital. Most of the children affected have Kawasaki disease, a rare vascular condition that is the main cause of acquired heart disease in under-18s in the UK. There are estimated to be 4.5 cases for every 100,000 children under the age of 18 in the UK. “These cases happen when someone with Kawasaki disease gets Covid-19 and that produces complications,” said one NHS source. In a letter to GPs in north London, reported by the Health Service Journal , NHS bosses said: “It has been reported that over the last three weeks there has been an apparent rise in the number of children of all ages presenting with a multi-system inflammatory state requiring intensive care across London and also in other regions of the UK. “The cases have in common overlapping feature of toxic shock syndrome and atypical Kawasaki disease with blood parameters consistent with severe Covid-19 in children. “There is a growing concern that a Sars-CoV-2-related inflammatory syndrome is emerging in children in the UK, or that there may be another, as yet unidentified, infectious pathogen associated with these cases.” A version of the warning has been sent by the Paediatric Intensive Care Society to all specialist doctors working in paediatric intensive care units in UK hospitals. The NHS letter adds that while some of the children did have Covid-19, others had tested negative for it. That could suggest that that group did not have it, or had had it, or that their tests were faulty. Describing the illness, the letter added: “Abdominal pain and gastrointestinal symptoms have been a common feature, as has cardiac inflammation. This has been observed in children with confirmed PCR positive Sars-CoV-2 infection as well as children who are PCR negative. Serological evidence of possible preceding Sars-CoV-2 infection have also been observed.” Sars-CoV-2 is the official name of the virus that causes the disease Covid-19. Doctors have been told to “please refer children presenting with these symptoms as a matter of urgency”. One intensive care doctor said: “There’s been an utterly unexpected uptick in severely sick children with a late inflammatory response that we think is related to Covid-19. It’s most unusual.” It is not known if any of the children have died. “This is not something people should be panicking about,” said Dr Liz Whittaker, a consultant at St Mary’s hospital in London and a member of the Royal College of Paediatrics and Child Health’s allergy, immunology and infectious diseases committee. Asked at the Downing Street daily press briefing about the reports, the health secretary, Matt Hancock, said they had left him “very worried”, while the government’s chief medical officer, Prof Chris Whitty, said: “This is a very rare situation but I think it is entirely plausible that this is caused by this virus, at least in some cases.” The condition came to light when doctors saw a number of unusual cases of children admitted to intensive care with a mix of symptoms from toxic shock and Kawasaki syndrome. The children had persistent fevers and severe abdominal pain and some had skin rashes. What concerned doctors most were blood tests that revealed severe inflammation, similar to that seen in adult patients with severe Covid-19 infections. Of the children admitted to intensive care, a number needed treatment for heart inflammation. “Our worry is that paediatricians who see children with fever and abdominal pain will do blood tests to look for problems such as appendicitis, but might not do bloods that look for inflammatory issues,” Whittaker said. Doctors suspect that the illness may be a “post-infection inflammatory response” where the immune system goes into overdrive. While some children have tested negative for coronavirus, they may have cleared the virus before the inflammation took hold, or the tests may simply have missed the infection. Prof Russell Viner, the president of the Royal College of Paediatrics and Child Health, sought to reassure parents that children are generally unlikely to become very unwell due to Covid-19. “We already know that a very small number of children can become severely ill with Covid-19 but this is very rare. Evidence from throughout the world shows us that children appear to be the part of the population least affected by this infection. “New diseases may present in ways that surprise us, and clinicians need to be made aware of any emerging evidence of particular symptoms or of underlying conditions which could make a patient more vulnerable to the virus. However, our advice remains the same: parents should be reassured that children are unlikely to be seriously ill with Covid-19, but if they are concerned about their children’s health for any reason they should seek help from a health professional.” The RCPCH’s guidance for parents on symptoms and seeking advice is available here.