Symptoms of a rare inflammatory condition have been identified in at least 15 children in New York City hospitals, alarming pediatricians across the country and raising concerns about a possible link to the coronavirus.

The patients exhibited symptoms typically seen in Kawasaki disease or toxic shock syndrome, including a persistent fever, according to the city’s health department.

The children were between 2 and 15 years old and were identified between April 29 and May 3. While all the patients had a fever, more than half of them reported a rash, abdominal pain, vomiting or diarrhea.

In an alert issued to doctors, the NYC health department said less than half of the patients exhibited respiratory symptoms. Four of the cases tested positive for COVID-19, while 11 tested negative.

No deaths have been reported, but many of the patients required blood pressure support and five of them required mechanical ventilation, the city’s health department said.

Both Kawasaki disease and COVID-19 are illusive conditions that doctors are still studying. Some experts doubt there’s a link between the two while others don’t believe the mysterious symptoms belong to Kawasaki at all.

What is Kawasaki disease?

“Kawasaki disease is one of the great mysteries in pediatrics,” said Dr. Frank Esper, a physician at the Cleveland Clinic’s Center for Pediatric Infectious Diseases. “It’s something we’ve been dealing with for decades.”

Symptoms include a fever of at least 101 degrees that lasts for five days or more, a rash and swollen glands in the neck, according to Britain’s National Health Service. Esper says that it predominately affects children between the ages of 2 and 6, tends to run during “mini-epidemics,” and is more likely to happen in the winter than the summer.

While doctors know how to treat Kawasaki disease, they still don’t know what causes it or why some people get it. Esper says “a cemetery of different reports” have hypothesized the disease is caused by viruses while others say people may be genetically predisposed.

“Kawasaki disease is the boogeyman to pediatricians,” he said. “It’s extremely difficult to diagnose. Even with the most astute clinicians, we have a hard time figuring out who has it and who doesn’t.”

Esper says the main indicator of the disease can be found in the heart. Coronary artery aneurysm, or a dilation of the coronary arteries, is what distinguishes Kawasaki from any other inflammatory disease.

First cases with COVID-19 concern appeared in Europe

The condition was first reported by doctors in Britain, Italy and Spain in late April. Britain’s Paediatric Intensive Care Society issued an alert noting there had been an increase in the number of children with “a multi-system inflammatory state requiring intensive care” across the country.

The group said there was “growing concern” that either a COVID-19 related syndrome was emerging in children or that a different, unidentified disease might be responsible.

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.

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.

Some possible cases have also been reported in France and Belgium.

Is Kawasaki disease related to the coronavirus? 

Experts say it’s too early to tell if the disease can be associated with COVID-19. 

“We’ve never seen the coronavirus before but we’ve been dealing with Kawasaki disease for decades,” Esper said.

He also said that experts aren’t even sure if the mystery disease popping up in parts of Europe and the U.S. can be definitively identified as Kawasaki disease. So far, he hasn’t seen any the reports mention coronary artery dilation, which would be a major indication. 

“I will caution that there are many things that look similar to Kawasaki disease,” Esper said. “It could be that what they’re calling Kawasaki is not Kawasaki but an inflammatory disease caused by the coronavirus.” 

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Dr. Sunil Sood, a pediatric infectious disease physician at Northwell Health’s Southside Hospital and Cohen Children’s Medical Center, doesn’t believe the condition is Kawasaki. 

Sood says patients he’s treated have been sicker, with inflammatory markers 10 to 100 times higher than average child with Kawasaki disease. 

Although the New York City Health Department only mentioned 15 cases in their alert, Sood says he’s had at least 20 cases between the two hospitals where he works. Only three of his cases tested positive for coronavirus with the regular PCR test, but the rest tested positive for coronavirus antibodies. 

He estimates his patients may have had the virus, even unknowingly, four weeks before developing the inflammatory condition. 

“The immune system can overreact in a delayed timeline many weeks later,” Sood said. “We know this from other infectious diseases.”

He advises parents and pediatricians to look out for a fever as well as a combination of any of these symptoms: Abdominal pain, confusion, diarrhea, red eyes, rash, swollen hands and feet, difficulty breathing and passing out. Sometimes the abdominal pain can be so severe that it mimics appendicitis. 

Sood urges parents to bring their children to the hospital if they develop any symptoms because it could lead to further heart complications, even acute heart failure.

“Initially, I thought it was Kawasaki … but it’s going beyond those symptoms,” he said. “Pediatricians and parents should be aware that there’s an outbreak of this right now.”

While there’s a spike in these cases, Sood says that children are still among the least affected group by the coronavirus. Data from more than 75,000 cases in China showed they comprised 2.4% of all confirmed cases and mostly suffered only mild symptoms.

Contributing: Associated Press. Follow Adrianna Rodriguez on Twitter: @AdriannaUSAT.