What to know about Kawasaki disease, a rare condition in children that doctors worry is linked to the coronavirus

• Kawasaki disease is a rare illness that causes inflammation in the walls of arteries throughout the body.
• The disease occurs in one in 10,000 children under the age of five annually, and is most often found in infants and children.
• It can be treated with high doses of aspirin or an IV drip of gamma globulin.
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Some 100 children in six European countries, as well as at least 25 children in New York City, have recently been hospitalized with symptoms that seemed similar to Kawasaki disease.

While no one has officially found a link between the rare condition, typically diagnosed in children, and the novel coronavirus, the WHO is "urgently" investigating a possible connection.

Doctors in the United States have been urged to be on high alert, as most of the children hospitalized in New York in recent weeks either had COVID-19 or had come into contact with it.

Here's what we know about the disease.

Kawasaki disease is a rare disease that primarily affects children under the age of five

The disease causes inflammation in the walls of the arteries throughout the body, and about one in 10,000 children under the age of 5 get the disease annually.

According to the CDC, the disease was first reported in Japan in 1967, and the first cases outside of Japan were reported almost a decade later. The disease is still 10 to 20 times more common in East Asian countries.

Symptoms of the disease include fever, rash, swelling of hands and feet, swollen lymph glands in the neck and irritation and inflammation of the mouth, lips, and throat.

The disease proceeds in phases, and the first one includes fever and skin rash, the second one involves skin peeling and abdominal pain, and in the third phase, signs and symptoms will slowly begin to go away.

Kawasaki disease can be treated with high doses of aspirin or an infusion of gamma globulin through the veins, the Mayo Clinic says. It is a leading cause of heart disease in children.

If left untreated, 15 to 25% of people with disease will develop thinning or bulging of the walls of the arteries that supply blood to the heart, which can be fatal, according to the US National Library of Medicine.

What causes Kawasaki disease?

Doctors still do not know what causes the disease.

Children with parents or siblings who had the disease are much more likely to get it, suggesting there could be a genetic link. According to the NHS, is unlikely that there is one gene that increases of the risk, and rather that it could be that various genes marginally increase the risk.

Kawasaki syndrome was poorly understood even before the coronavirus pandemic, but seems to be triggered by viruses or infections, as Business Insider's Mia Jankowicz previously reported.

"Kawasaki syndrome does not have a precise cause, but in genetically predisposed children there is a triggering environmental factor, probably infectious and probably viral," pediatrician Dr Marianna Fabi, who is treating five cases at Bologna's Sant'Orsola-Malpighi hospital, told Il Corriere Della Sera.

However, to date no one strain of bacteria or virus has been identified as a clear trigger for the condition.

Some doctors suspect there may be a link between COVID-19 and Kawasaki disease

Doctors are currently calling the illness that has sent children all over the world to the hospital a "pediatric multisystem inflammatory syndrome." In New York, at least five patients with the syndrome needed ventilators, and others needed blood pressure support.

"If your child is experiencing a persistent fever, rash, abdominal pain or vomiting, call your doctor right away," New York City mayor Bill de Blasio tweeted.

Dr. Roshni Mathew, pediatric infectious disease specialist at Stanford's Lucile Packard Children's Hospital, told TIME "the general thought is this is a post-infectious trigger causing the immune system to hyper-react." Any infection, including the new coronavirus, can cause an inflammatory response like Kawasaki disease.

"From what we understand, this is a rare complication in the pediatric population that they believe is related to Covid-19," New York State health commissioner Howard Zucker told the NYT.

To the Guardian, Dr. Liz Whittaker, a member of the Royal College of Paediatrics and Child Health's infectious diseases committee, said that "this is not something people should be panicking about."