Having a cold or the flu may sometimes trigger a stroke in children -- particularly those with underlying health conditions -- though the overall risk remains low, a new study indicates.
Comparing two groups of more than 350 children -- one set had suffered "ischemic" clot-based strokes and the other had not -- researchers found that those with stroke were six times more likely to have had a minor infection the previous week than those who didn't have a stroke.
Also, children who had most or all of their routine vaccinations were significantly less likely to suffer a stroke than children who received only some or no vaccinations, according to the study, published online Sept. 30 in the journal Neurology.
"The findings are definitely revelatory in terms of expanding our understanding of childhood stroke compared to a decade ago," said study author Dr. Heather Fullerton, a professor of child neurology and pediatric stroke neurologist at University of California, San Francisco (UCSF), Benioff Children's Hospital in San Francisco.
"It basically offers some explanation why a stroke may happen on a particular day in a child's life, and offers an opportunity for stroke prevention," Fullerton added. "You can't change a child's underlying condition, but you can potentially do something about that stroke trigger."
However, the study merely showed an association between minor infections and children's stroke risk, but didn't prove a cause-and-effect relationship.
Stroke in children is exceedingly rare, occurring in two to 13 out of every 100,000 children annually. Most of those children cope with underlying health conditions such as congenital heart disease, sickle cell anemia or a blood-clotting disorder. Only about one in 100,000 otherwise healthy children suffer a stroke each year, Fullerton said.
Stroke symptoms in children are typically similar to those in adults, including slurred speech, facial drooping and arm weakness. But adults' risk factors for stroke are much different than children's, arising mainly from factors such as high blood pressure, diabetes and smoking.
In the study, Fullerton and her team reviewed medical charts and conducted parent interviews of 355 children up to age 18 (average age 7) diagnosed with a stroke and 354 stroke-free children of similar ages. The groups hailed from nine countries. Researchers analyzed the children's exposure to infection and their vaccine history.
Of all participants, 18 percent of those with stroke had an infection -- including flu, colds, or to a lesser extent, urinary tract or gastrointestinal infections -- in the prior week. Only 3 percent of the children who didn't have a stroke had had an infection the week before. The association between infection and stroke was short-lived, lasting no longer than a week, experts noted.
Meanwhile, children who had received some, few or none of their routine vaccinations were seven times more likely to have a stroke than those who received most or all of their vaccinations.
"Vaccines are clearly protective," Fullerton said. "No matter how we cut the data ... vaccines always appear to protect against childhood strokes."
How a minor infection might trigger a stroke is not entirely clear, neurologists said. But it's possible that an infection may set off an inflammatory process throughout the body that contributes to stroke, revving up clot formation. Dehydration during an illness could also play a role, they said.
Fullerton, also director of the Pediatric Brain Center at UCSF, said that even otherwise healthy children can suffer a stroke, "but when lightning strikes, and that previously healthy kid has a stroke, we're still trying to better understand why."
"This is definitely not something for parents to worry about," she added. "If your child is otherwise healthy, your child's risk of having a stroke is very low. It's not zero."
Dr. Stephen Eppes, vice chair of the department of pediatrics and director of pediatric infectious diseases at Christiana Care Health System in Wilmington, Del., said he was "a little bit struck by the results" of the study.
"Obviously the burden of stroke in the pediatric population is much lower than the adult population," said Eppes. "But the study authors ... have hit on something."
But, Eppes added, "I would try to put things in perspective for parents and tell them that illnesses with fever are much more likely to represent something bad from an infection point of view than from a stroke point of view. Minor infections ... are usually not associated with stroke to an extent anyone should worry about."
Dr. Jose Biller, chair of neurology at Loyola University Chicago Stritch School of Medicine, wrote an editorial accompanying the new research that said the findings will be pivotal in defining further stroke prevention strategies in children.
"I think further studies will be needed, but this was a very well-conducted study, particularly in a population that has been less well-studied [than] adults with stroke," said Biller.
In addition to making sure children receive all routine vaccinations, including for flu, parents and teachers can remind children of easy ways to avoid passing along colds and other infections, Fullerton said.
"Common infection-control measures like hand-washing and covering their mouths are going to be helpful in these kids," she said. "Even teaching kids to cough into their elbow rather than their hand ... can actually make a big difference to protect kids we know to be at increased risk."