A dozen US states have raised concern about the spread of an unusual virus that is striking children with severe respiratory illness in clusters, but not adults, health officials said Monday.
The culprit in most cases identified so far is enterovirus 68, or EV-D68, said assistant surgeon general Anne Schuchat.
She said "about 12 states" have reported apparent clusters to the US Centers for Disease Control and Prevention.
"The situation is evolving quickly," she said. "I wouldn't be surprised if there are many more."
No deaths have been reported this year, but infants, children and teenagers are most vulnerable, and some states have seen a spike in hospitalizations, she said.
According to US media reports, the affected states include Colorado, Georgia, Illinois, Iowa, Kansas, Kentucky, Missouri, North Carolina, Ohio and Oklahoma.
"This isn't a new virus," Schuchat told reporters, noting that it was first discovered in 1962.
However, it "is fairly uncommon, and we don't know as much about it as we do about some of the other common enteroviruses," she said.
"It can cause mild or severe respiratory illness, yet the full spectrum of all of the illnesses it can cause are not well-defined, and that is something people are looking into with these clusters."
Clusters of EV-D68 have also been seen recently in Japan and the Philippines, she said.
While EV-D68 was reportedly uncovered in some tests in children who were afflicted with a polio-like syndrome earlier this year, Schuchat said no neurological symptoms have been seen in this summer's US cases.
"I'm not aware of new severe neurologic symptoms being linked with this strain. As of this summer's investigation we have not seen that," Schuchat said.
The virus likely spreads from person to person when an infected person coughs or sneezes, or when someone touches an infected surface.
There is no vaccine against enterovirus-D68, and experts do not understand why it is emerging and spreading now.
Hand-washing and good hygiene are considered the only ways to prevent its spread.
A report from the Centers for Disease Control released Monday detailed initial reports of severe respiratory illness clusters in Kansas City, Missouri and Chicago, Illinois last month.
Schuchat said 19 of 22 specimens in Kansas City and 11 of 14 from Chicago tested positive for EV-D68. The age of those infected ranged from six weeks to 16 years.
All of the Kansas City patients and 10 of 11 Chicago cases were sent to a pediatric intensive care unit for respiratory distress.
"We are just beginning to understand the clusters in Kansas City and Chicago," Schuchat said, declining to give a complete number of cases.
Sampson Davis, an emergency room physician at New Jersey's Meadowlands Hospital Medical Center, said parents should seek help if they notice their child has trouble breathing.
"Children in particular with asthma or respiratory illnesses are impacted more by this virus," said Davis.
Parents should seek emergency care "when a child has increased difficulty breathing, uncontrollable cough and shortness of breath," he said.