LONDON — U.K. paediatrics specialists have warned that a small but rising number of children are becoming ill with a rare syndrome that could be linked to coronavirus.

On Sunday the Paediatric Intensive Care Society UK (PICS) warned about a small rise in the number of cases of critically ill children, some who had tested positive for COVID-19, presenting "overlapping features of toxic shock syndrome and atypical Kawasaki disease with blood parameters."

In a statement sent over the weekend to medical professionals who look after critically ill children, PICS said "abdominal pain and gastrointestinal symptoms have been a common feature as has cardiac inflammation."

Spain’s Association of Pediatrics recently made a similar warning, telling doctors that in recent weeks, there had been a number of school-age children suffering from “an unusual picture of abdominal pain, accompanied by gastrointestinal symptoms” that could lead within hours to shock, low blood pressure and heart problems.

“It is a priority to recognize these (symptoms) to urgently refer these patients to a hospital,” the pediatric association said.

In Italy, Dr. Angelo Ravelli of Gaslini Hospital and a member of the Italian Paediatricians’ Society, sent a note to 10,000 colleagues raising his concerns. He and his team reported an unusual increase in the number of patients with Kawasaki disease in regions of Italy hit hard by the pandemic, noting some children had COVID-19 or had contacts with confirmed virus cases.

“These children do not respond to traditional treatment,” he said, adding that some were given a high dose of steroids. Those who developed toxic shock syndrome needed help breathing and were admitted to intensive care units, Ravelli said.

So what is Kawasaki disease and how worried should parents and carers be?

What is Kawasaki disease?

Kawasaki disease, also known as Kawasaki syndrome, is a rare childhood illness that causes the walls of the blood vessels in the body to become inflamed.

According to the U.K.'s National Health Service (NHS), the condition -- also known as mucocutaneous lymph node syndrome -- mainly affects children under the age of 5, although it can affect children of any age.

Symptoms include a high temperature lasting for five days or longer, alongside a rash, swollen glands in the neck, dry cracked lips, red fingers or toes and red eyes, according to the healthcare provider.

If treated, the symptoms usually become less severe, the NHS said, adding that the disease is not contagious.

"Thankfully Kawasaki-like diseases are very rare, as currently are serious complications in children related to COVID-19, but it is important that clinicians are made aware of any potential emerging links so that they are able to give children and young people the right care fast," Professor Simon Kenny, NHS national clinical director for children and young people said in a statement sent to CNN on Monday.

A condition that can lead to heart complications

Kawasaki disease is a leading cause of acquired heart disease in the United States, and serious complications can include aneurysms and coronary artery dilations, according to US healthcare company the Mayo Clinic.

Standard treatment, which involves intravenous immunoglobulin and aspirin, can substantially decrease the development of coronary artery abnormalities, the US Centers for Disease Control and Prevention (CDC) says.

According to the NHS, around 25% of children with the disease who do not receive treatment go on to experience heart complications, which can include conditions such as heart attacks and heart disease.

However, the health care provider says that most children with Kawasaki disease make a full recovery if they receive prompt treatment.

What causes Kawasaki disease?

Experts admit that the causes of Kawasaki disease are not fully understood, but think that children who develop it could be genetically predisposed to it, having inherited certain genes from their parents.

The disease itself is not contagious, according to the NHS, meaning that it is unlikely to be caused by a virus alone.

The disease is more common in children from Northeast Asia, especially Japan and Korea, the NHS said.

What is the link to COVID-19?

The link between Kawasaki disease and COVID-19 is unclear, but health care professionals have reassured parents that the risk of children becoming severely ill with the virus remains low.

In a report released in April, the CDC said that children diagnosed with coronavirus in the US typically have mild cases of the virus.

The number of COVID-19 cases among children remains small and while some children and infants have been sick with COVID-19, adults make up most of the known cases to date, according to the CDC.

Professor Rosalind Smyth, director and professor of child health, UCL Great Ormond St Institute of Child Health, said current evidence suggests that most children with COVID-19 who receive medical attention have mild symptoms, with about half having a fever, around 40% having a cough and less than 10% of reported cases having gastrointestinal symptoms.

"However, our understanding of this condition in children is limited. COVID-19 does present, in adults, as an inflammatory disease affecting a number of organs. We should investigate fully these children, with SARS-CoV-2, who present with a multi-system inflammatory disease to assess whether this is a presentation of COVID-19," Smyth said in a statement Monday.

The Associated Press contributed.

First Published: April 29, 2020, 8:30 a.m.