NEW YORK - Small children, with their image of runny noses and dirty hands, may be unfairly vilified for their role in spreading sickness, according to a study.

Instead, teens and young adults may be the main drivers of seasonal and pandemic flu, a report in the American Journal of Epidemiology said.

Flu cases tended to peak in Canada in the 10-to-19 and 20- to-29 age brackets before the disease topped out in older adults or young children during seasonal and pandemic flu outbreaks - meaning prevention in this age group may be key to slowing transmission of flu on a bigger scale.

"For seasonal influenza, both the 10-19 and 20-29 year age groups peaked one week earlier than other age groups, while during the fall wave of the 2009 pandemic, infections peaked earlier among only the 10-19 year age group," wrote lead researcher Dena Schanzer, of the Public Health Agency of Canada.

"This analysis casts doubts on the hypothesis that younger school-age children actually lead influenza epidemic waves."

Schanzer and her team collected data from positive lab tests for the flu compiled by the Canadian government every year. Then they graphed the number of flu cases in children and adults of different ages over the course of each flu season, allowing them to see when the flu peaked in each group and which group "led" the epidemics.

In the years between 1995 and 2006, they found that seasonal flu peaked in the 10-19 and 20-29-year-olds about one weak earlier than it did in older adults and young children.

During the 2009 H1N1 epidemic, flu cases hit their peak in preteens and teens a few days before other groups as well.

Schanzer and her colleagues wrote that the didn't have enough data to figure out why teens and young adults might have been leading the epidemics in Canada. Other studies have found that preschoolers might lead the way in spreading flu.

Researchers, though, speculate that school-age children and young adults might have more close contact with a greater number of peers than very young children.

"The really small kids, they're certainly extremely susceptible (to the flu) in general, but they're not as mobile and they don't congregate in as large a group as middle school and high school kids do," said Ira Longini, who studies infectious diseases at the University of Washington School of Public Health in Seattle.

It may be the same with young adults, who tend to be socially active, he added.

But in general, "what we believe happens is these outbreaks start in the schools and rapidly get into families and then radiate out from there to workplaces and other settings," Longini, who was not involved in the latest study, said.

"It's really households and schools that drive these epidemics."

Every year, between five percent and 20 percent of US residents get the flu, contributing to some 36,000 deaths. To stop the spread of the virus, Longini said that elementary, middle and high school-age children need to be the target of flu prevention efforts.

"We need to use vaccines effectively and early in the season to vaccinate school children," he said.

"We just need to do that every fall if we want to slow (the transmission of) influenza."