A rare virus — enterovirus D68, also known as EV-D68 — is infecting more than 500 children across the country and sending them to hospitals with severe respiratory infections and breathing problems.
The virus was also detected in the bodies of five children who died.
Now, the Centers for Disease Control and Prevention (CDC) is warning doctors and parents to be on the lookout. Here's what we know and what we don't know so far.
What we know
— As of October 6, 594 people in 43 states have been infected with EV-D68. There have also been confirmed cases in Canada. And the virus shows no sign of slowing down. Investigations into suspected clusters in "many other states" are ongoing, according to the World Health Organization.
— Five children infected with EV-D68 have died since late September. The CDC has not been able to say whether the enterovirus was the cause of death. Four of those children showed symptoms of EV-D68 prior to their death. Another child died in his sleep but he had no symptoms prior to his death. Officials later confirmed he had EV-D68, and said brain and lymph node swelling was the result of the virus.
— Cases so far involve young kids of both sexes, many of whom had a history of asthma or wheezing. So the virus appears to be affecting those with underlying health issues. The kids stricken with EV-D68 had difficulty breathing and a good number of them experienced wheezing. They also had low blood-oxygen levels. Fevers were less common.
— There's not much you can do to treat it. There are no vaccines or antiviral treatments for EV-D68. The main kind of care is just supportive, which means paying attention to symptoms and making sure people get proper fluids and help breathing, if necessary. The CDC's Dr. Anne Schuchat said she believes the virus typically runs its course in a week.
Dr. Pritish Tosh, an infectious diseases physician-researcher at the Mayo Clinic, added: "When dealing with respiratory illnesses in young people, they can be severe and result in hospitalizations and the requirement of intensive care. And it looks as through this strain of the virus is causing infections in children severe enough to get them admitted to the hospital."
— Enteroviruses generally are very common. They usually turn up as "summer colds." There are more than 100 different strains, and they affect between 10 and 15 million people in the US per year. They can cause everything from encephalitis to viral meningitis.
— This particular strain of enterovirus is rare, which means scientists don't know a whole lot about it, making its sudden appearance concerning. It was first identified in California in 1962. Compared to other strains of the enterovirus, it has been uncommon in the US. The CDC said that during 2009-2013, they got 79 reports of EV-D68 and it has been the cause of small clusters of sickness but never a widespread outbreak like the one that seems to have taken hold across the country.
— EV-D68 spreads like the common cold through respiratory secretions, such as coughing, sneezing, or touching an infected surface.
— Symptoms of EV-D68 are believed to be similar to respiratory illness, like a really severe cold. Though the full spectrum of sickness that this strain can bring on is unclear. "We don't know as much about it as we do about some of the common respiratory viruses," said the CDC's Dr. Schuchat.
— EV-D68 may cause Polio-like paralysis and limb weakness. Health officials aren't yet certain about whether the virus cases paralysis in children, or whether it's an association, but the link between the virus and the symptom has been found in several cases this year.
— EV-D68 is detected using molecular techniques at several labs across the US and it's not monitored nationally. According to the CDC, enterovirus infections including EV-D68, are not required to be reported.
— The CDC says health care providers should be on the lookout for EV-D68 as a possible cause of serious and unexplained severe respiratory illness. Parents should only worry if their kids are having difficulty breathing. If your child is having trouble breathing, see a doctor. Good hygiene — washing hands regularly and covering coughs — can help prevent the disease's spread.
— The virus should die down soon. We are currently in the middle of the enterovirus season. EV-D68 infections are likely to decline later in fall.
What we don't know
— We don't know why this strain has turned up in these geographic locations. Again, EV-D68 is thought to be rare so why it's turning up now and landing kids in hospitals, is unclear.
In a statement to Vox, the CDC said: "In the United States, people are more likely to get infected with enteroviruses in the summer and fall. The spread of enteroviruses is often quite unpredictable. A mix of enteroviruses circulates every year, and different types of enteroviruses can be common in different years. This year the number of people with confirmed EV-D68 infections is much greater than that reported in previous years. It appears to be the predominant type of enterovirus this year and may be contributing to increases in severe respiratory illnesses."
— How deadly it is. Since it's not a reportable disease, the CDC said it "does not know how many infections and deaths from EV-D68 occur each year in the United States." Local officials are investigating the five EV-D68-related deaths to try to better understand what role the virus played.
— Public health officials are not sure about all the symptoms this strain of the virus can cause, since it's uncommon. That means EV-D68 may cause other types of illness beyond just respiratory complications, but we just don't know yet.
— Exactly who is most at risk. The CDC said, "In general, infants, children, and teenagers are most likely to get infected with enteroviruses and become ill. That's because they do not yet have immunity (protection) from previous exposures to these viruses. We believe this is also true for EV-D68." Kids with asthma seem to be more affected.
If you have more questions about enterovirus, send them to julia.belluz@vox.com or tweet them @juliaoftoronto