Scientists have found the first clear evidence that infection with coronavirus causes the Kawasaki-like inflammatory condition affecting children. 

A study of eight children admitted to a Birmingham hospital with the condition reveals they were infected with the SARS-CoV-2 virus several weeks before showing symptoms. 

All of the children tested negative in the traditional lab-based test used to diagnose COVID-19 in adults.

However, a custom-built antibody test revealed the young patients had been infected with the coronavirus and produced antibodies to fight off the pathogen. 

Doctors who treated the children say antibody tests are the only way to accurately identify the presence of the virus in children suffering with the hyperinflammatory condition, which can be fatal.

It remains unknown why the syndrome develops weeks after infection, but scientists believe it may be due to a severe overreaction from the body's own immune system. 

This 'immune-mediated pathology' causes the immune system to go haywire and can cause damage to the body's own cells.

A similar phenomenon has been seen in adults, and it can be fatal to the sickest patients. 

The syndrome affecting children has been tentatively called PIMS-TS, for 'paediatric inflammatory multisystem syndrome temporally associated with SARS-CoV-2'. 

However, the British scientists say this name is incorrect as it is not 'temporally associated' with the pandemic but is instead 'triggered by SARS-CoV-2 infection'. 

A team of scientists led by Dr Alex Richter and Professor Adam Cunningham of the University of Birmingham studied eight young patients who were admitted to hospital between April 28 and May 8. 

Lab tests — which are used to identify COVID-19 and also to screen healthcare workers — came back negative for all eight individuals. 

These tests, called PCR tests, are extremely reliable and are 'the nearest to a gold standard for determining active infection'.

The average age of the children admitted to hospital was nine years old and five of the patients were boys. 

Seven of the patients showed symptoms of both hyperinflammation and Kawasaki disease.

One of the patients was expressing symptoms of hyperinflammation as well as some signs of toxic shock syndrome.  

The mysterious and dangerous condition is being described by top medical professionals as very rare and symptoms can include fever, abdominal pain, rashes and red lips and eyes.

A very small group go into shock, in which the heart is affected, and they may get cold hands and feet and have rapid breathing.   

Of the eight children treated in Birmingham and studied as part of this landmark research, all patients had fever and at least one gastrointestinal symptom such as abdominal pain, vomiting and diarrhoea.

Six of the patients required admission into paediatric intensive care due to heart-related issues and low blood pressure brought on by the disease.

All showed positive signs after treatment and have since been discharged from ICU.

Due to the reports in the media and claims from leading advisers and prominent politicians that this condition may be linked to the coronavirus pandemic, the researchers took blood samples for analysis from all eight children.  

They then developed an custom antibody test with the help of researchers at the University of Southampton.

The test involves making an artificial copy of a key protein on the surface of the coronavirus which looks like a spike.

This unique 'spike' is a key identifier of the killer virus and was first revealed in detail by Professor Max Crispin of the University of Southampton.

He modelled the protein's surface spikes and this has allowed his team to produce an almost exact copy of the spike.  

In the Birmingham hospital, this artificially created version of the protein spike was mixed with blood samples from the patients. 

The researchers saw that some antibodies in the blood of the children bound to the spike, in the same way they would if the virus itself was invading.  

In the tests, researchers looked to see which of three different immunoglobulins (the technical name for an antibody) - IgG, IgA and IgM - locked onto the imitation virus. 

A positive IgM reading in the tests indicates a recent infection whereas a positive reading for IgG and IgA shows an older infection, the scientists say.

The children in the Birmingham hospital had no IgM antibodies but did have IgG and IgA antibodies, showing that they were infected with SARS-CoV-2 several weeks previously.

This time delay is the reason the PCR test did not detect the infection, the researchers say. 

'IgM was not detected in children, which contrasts with adult hospitalised adult COVID-19 patients of whom all had positive IgM responses,' the researchers write in the study, which has been submitted to a preprint server and seen by MailOnline.

'For antibody responses, IgM responses develop first, before eventually waning and IgG responses dominating thereafter,' the researchers explain. 

'Thus, high levels of IgG in the absence of IgM are typically suggestive of infection weeks or even months previously. '

This antibody test is conducted in a laboratory and is not a portable test. It is also fundamentally different to the test approved by the government today, which is manufactured by Roche. 

Roche's method uses a nucleoprotein to mimic the SARS-CoV-2 virus, not the viral spike.  

'Using the native-like viral spike for antibody testing is proving a highly sensitive way of detecting exposure to SARS-CoV-2,' Professor Crispin told MailOnline.   

The researchers say their research shows that the only way to diagnose patients with symptoms of severe inflammatory syndrome who have tested negative for the PCR is via antibody testing. 

'This is important, as until now, serology has not been useful diagnostically, only for epidemiology. 

'This therefore offers a widening of the value of serology in the identification and understanding of infections caused by SARS-CoV-2.

'Indeed, since all patients were positive serologically, it may be worth considering amending the definition of PIMS-TS so that TS is not just "temporally associated with SARS-CoV-2 pandemic", but "triggered by SARS-CoV-2 infection",' the researchers conclude.