A mother's hand feeling the forehead of a sick child / REX/Monkey Business Images

The illness has affected children across 10 US states

Hundreds of children across 10 US states - some of whom are in intensive care - are being treated for a severe respiratory illness known as Enterovirus 68.

As experts attempt to understand why the outbreak has been so widespread, we explain everything you need to know about the illness.

What is the Enterovirus 68?

Enterovirus is the name of more than 100 of the most common viruses that affect humans and other mammals - including the common cold, according to the Washington Post . The ‘68’ signifies the order in which the particular strain was discovered, the first identified in 1962.

Also known as VD-68 or Enterovirus D68, this member of the viral family typically strikes during the summertime through to autumn.

“It's not highly unusual but we're trying to understand what happened this year in terms of these noticeable and much larger clusters of severe respiratory disease,” Mark Pallansch, director of the viral diseases division at the federal Centers for Disease Control and Prevention has said of the situation.

What are the symptoms?

Patients can suffer from mild cold-like symptoms, but this summer's cases are unusually severe, said Pallansch.

The illness can escalate quickly, causing a fever, coughing, wheezing and low blood oxygen levels (also known as hypoxemia).

Enterovirus 68 can also exacerbate other respiratory problems such as asthma and can see patients become so ill they require breathing aids.

But this outbreak has seen children without asthma developing breathing problems usually associated with the disease, Pallansch said.

Video: Enterovirus breaks out in the US

Rafal Tokarz, a scientist at Columbia University's Center for Infection and Immunity who has studied the spread of Enterovirus 68 told the Washington Post that while adults do contract the virus, their symptoms may not be as severe meaning the illness can go undetected.

How is it spread?

Like the common cold, Enterovirus 68 spreads when an infected person coughs or sneezes, allowing the virus to come into contact with the nose or mouth of an uninfected person.

Is there a treatment for Enterovirus 68 and does it have long-term effects?

There is no treatment for the virus or any anti-viral medicine, but luckily most cases are not fatal. Intensive treatment and supportive care, including oxygen, can help. On average, patients are hospitalised with the illness for one to five days. 

Most children recover with no lasting problems.