A rare form of a virus that causes respiratory illness has spread among children across the United States, creating a medical emergency in the states that it has been detected in. A majority of blood samples taken from children at hospitals in Kansas City and Chicago have tested positive for EV- D68, a form of non-polio enterovirus.

A dozen states -- Alabama, Colorado, Michigan, Georgia, Ohio, Iowa, Illinois, Missouri, Kansas, Oklahoma, Kentucky and Utah -- have now reported several children who are showing signs of having contracted the illness. So far, samples collected from six of the 12 states -- Colorado, Kansas, Kentucky, Illinois, Missouri and Iowa -- have tested positive for EV-D68, according to CNN.

This particular form of virus has rarely been reported in the U.S., and the Centers for Disease Control and Prevention, or CDC, said Tuesday that Missouri and Illinois have reported more children with EV-D68 than any other state. Ann Schuchat, director of CDC’s national center for immunization and respiratory diseases, also confirmed Tuesday that 19 of the 22 samples collected from Kansas City and 11 of the 14 samples from Chicago had tested positive for EV- D68.

“This is a dynamic situation, unusual virus. On a backdrop of very common of respiratory viruses and we are just beginning to understand the clusters in Kansas City and Chicago,” Schuchat said, in a briefing Tuesday, adding: “We understand the concern about this situation. Severe respiratory illness is always a concern to us, especially when children are affected.”

Last week, hospitals in Illinois and Missouri had barred healthy children from entering buildings, in an effort to contain the spread of the enterovirus. Doctors now also fear and suspect that the disease is spreading faster after schools have reopened following the summer break.

Here’s a breakdown of facts about EV-D68, the rare strain of the enterovirus.

What is Enterovirus?

It is a family of viruses that causes infections including fever, runny nose, sneezing, cough, skin rash, mouth blisters, and body and muscle aches. But, in a few severe cases, the patient can contract heart and brain infections, paralysis or meningitis. According to the CDC, more than 10 million to 15 million enterovirus infections occur in the U.S. annually.

What Is EV-D68?

EV-D68 is a specific virus of the enterovirus family, which causes mild-to-severe respiratory problems and was first discovered in California in 1962. Because this form of the virus is less frequently identified, there is not much information available about this particular strain. However, the CDC says that it is studying the virus closely.

What are the symptoms of the EV-D68 virus?

While most people affected by it do not show a specific symptom, wheezing and severe breathing problems are common. But, only about 30 percent of children infected by the virus develop a fever.

How can it be prevented and cured?

EV-D68 spreads from contact with an infected person and there is no specific treatment or vaccine available yet. But, the CDC recommends influenza vaccines for people who have not taken it for more than six months, to counter flu viruses in the air. People can also avoid the disease by disinfecting touched surfaces, avoiding close contact with infected patients and by washing hands often.