Stroke is rare in children, but the risk of it happening is increased when a child has a cold or the flu, and reduced when kids are fully vaccinated, according to a new study.

Based on 700 children across nine countries, researchers linked having had a recent illness like bronchitis, ear infection or "strep throat" to a six-fold rise in stroke risk. Having few or none of the routine childhood vaccinations was tied to a seven-fold rise in risk.

"We're always trying to raise awareness that childhood stroke happens at all," said lead author Dr. Heather J. Fullerton of UCSF Benioff Children's Hospital San Francisco.

It is more common in kids who have other risk factors, like congenital heart disease or sickle cell disease, Fullerton told Reuters Health. Some parents of children with chronic conditions wonder if it is safe to vaccinate their kids, and these results indicate it is even more important that they do.

Parents should be reassured to know that infection prevention measures like hand washing and vaccines can help prevent stroke as well, she said.

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From birth to age 19 years, the rate of strokes among youth in the U.S. is about five per 100,000 children. In comparison, about three in 100 adults aged 45 to 65 have a stroke each year, according to the Centers for Disease Control and Prevention.

Up to 40 percent of kids who have a stroke will die from it, according to the American Stroke Association.

Fullerton and her coauthors used medical records and parental interviews for 355 children under age 18 who experienced a stroke and compared them to records and parental interviews for 354 children without stroke.

Half of the children with stroke were age seven or older.

In the stroke group, 18 percent of the children had contracted some kind of infection in the week before the stroke occurred, while three percent of children in the comparison group had an infection in the week before the study interview.

Stroke risk was only increased for a one-week period during infection. Infections a month earlier were not tied to stroke risk, according to the results in Neurology.

"There's been suspicion about a link between infection and stroke for a while, moreso in adults," she said. "But whenever it was brought up, people always questioned whether cold medications played a role."

According to this analysis, the infection itself triggers the stroke, not cold medicines, which were used infrequently by parents in the study.

"When you have an infection, the body mounts immune response," which manifests as fever, aches and blood that clots more easily, Fullerton said.

In stroke, a blood clot blocks blood flow to the brain.

"One can speculate that changes in the body as a result of infection may tip the balance in a child already at higher risk for stroke," said Dr. Jose Biller, chair of neurology at the Loyola University Chicago Stritch School of Medicine, who coauthored an editorial in the same issue of the journal.

"Parents should not be alarmed if their child has a cold that this will lead to stroke," Biller told Reuters Health.

But they should be encouraged to continue with routine infection prevention practices, including the regular pediatric vaccine schedule, he said.

"Most physicians will agree that vaccines are among the safest medical products, they are rigorously tested and monitored," he said. "They prevent thousands of illnesses and deaths in the U.S. each year."

Infants with stroke generally present with seizures, while older infants and school age kids with stroke will have similar symptoms to an adult, including weakness on one side of the body, Fullerton said.

Parents may recognize these as stroke symptoms but believe children don't have strokes, so delay calling an ambulance, she said.

"If you ever think your child is having a stroke, call 911 (emergency services)," she said.

SOURCE: http://bit.ly/NwhhyY Neurology, online September 30, 2015.