The culprit is Enterovirus 68 (also known as EVD-68 or Eentrovirus D68), a rare viral infection that can cause symptoms such as coughing, wheezing and low blood oxygen levels (also known as hypoxemia). In some cases, however, the symptoms can be severe — particularly for children who already suffer from asthma or other respiratory problems.
Jennifer Cornejo of Colorado told Denver's ABC affiliate that her 13-year-old son, William, had cold symptoms that developed overnight into a life-threatening illness. "He was in really bad shape," she told the station. "He came really close to death. He was unconscious at our house and white as a ghost with blue lips — he just passed out."
Here is how William Cornejo described it: "My head started hurting. And after that my lungs started closing up. It felt different."
Until recently, Enterovirus 68 was only thought to cause sporadic infections, but there have been reports of more widespread outbreaks in Georgia, Pennsylvania and Arizona between 2008 and 2010.
Only Missouri and Illinois have confirmed cases of EV-D68, but cases with similar symptoms have been reported in Colorado, Georgia, Iowa, Kansas, Kentucky, North Carolina, Ohio and Oklahoma, as well. Cases of EV-D68 have also been confirmed in Canada.
The outbreak, though worse than usual, is typical for this time of year, and the CDC expects that cases will decline in the fall. In the mean time, here is what you should know now:
Why is it called Enterovirus 68?
Enterovirus is the name used to describe a group of more than 100 of the most common viruses that affect humans and other mammals. Most people might interact with an enterovirus by way of the common cold, which can be caused by enteroviruses as well as rhinoviruses.
Enterovirus 68 got its number based on the order in which it was discovered. The first cases were identified in California in 1962 in four children who had bronchitis and pneumonia. Since it was discovered, and through 2005, there were only 26 confirmed reports of the virus to the Centers for Disease Control and Prevention.
How did it spread so quickly?
Enterovirus 68 spreads like the common cold: coughing, sneezing, or touching people or things infected with the virus and coming into contact with the nose or mouth.
With the start of school in late August and early September for most children in the United States, spreading the disease is more likely than ever.
"This is the right time of year for enterovirus infections," said Anne Schuchat, Assistant Surgeon General and Director, of the National Center for Immunization and Respiratory Diseases with the CDC. But she added that the number of potential cases is "higher than expected for this time of year."
But because there isn't much known about this virus, it is possible that Enterovirus 68 is more contagious than it was believed to be.
Since it was discovered in the 1960s, the virus has evolved, making it likely that how it is spread has also changed, said Rafal Tokarz, a scientist at Columbia University's Center for Infection and Immunity who has studied the spread of Enterovirus 68.
"We speculate that this virus in the past 10 to 15 years has sort of evolved into different sub types and has allowed it to become more prevalent worldwide," he said. "Maybe it has mutated into something that is more easily transmissible, I don’t know if that is the case but it's certainly possible."
Why are children getting sick but not adults?
So far, all of the confirmed cases of this virus have been in children, the CDC said, but the Enterovirus can also affect adults. According to the CDC, approximately a quarter of all Enterovirus 68 cases before 2005 were adults.
It is possible that the respiratory symptoms are more acute among children than adults. Kids, particularly if they suffer from asthma or other respiratory problems, might become so sick that they require a trip to the emergency room where they can be treated with breathing aids.
"It was initially believed to be associated mostly with kids, but there have been reports that it can also appear in adults," said Tokarz. "In adults, the symptoms may not be as severe, which is why in some cases the symptoms may be missed."
How do I know if my child has it?
Enterovirus 68 is just one of many potential causes of respiratory illness. And the only way to know if someone has this particular type of virus is through a form of testing that sequences the virus. If a child reports severe difficulty breathing, and especially if that child also suffers from asthma, parents should consult a health care professional.
Many hospitals are able to do this kind of testing, but if they cannot, they can send samples to the CDC, which has the ability to conduct more advanced testing and confirm an infection.
Is there treatment or a cure?
There is no treatment that is specific to the virus, and there are no anti-viral medications. But most cases of the virus are not fatal. Intensive treatment and supportive care, including oxygen provided in a hospital setting help. And in the confirmed cases of Enterovirus 68 from 2008 to 2010, the median length of time patients were hospitalized ranged from 1.5 to five days.
How do we stop it from spreading?
Other than treating the symptoms of patients who have contracted the virus, there is very little that can be done to stop the spread of EV-D68.
But practicing normal, good hygiene is more important now than ever. Washing hands, disinfecting surfaces, avoiding touching eyes, mouths, and noses with dirty hands can all help stop the spread of the virus. And if you or your child feels sick, stay home rather than risking further spreading the virus at work or at school.
Sarah Kaplan contributed to this report.
[This post has been updated.]