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Health

Another Thing to Blame on the South: Your Flu

Scientists recently tried to determine the origins of eight different outbreaks.
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Flu season—and the gnarly symptoms that accompany it—are an inevitability every winter. But until recently, why the annual outbreak of influenza occurs, as well as how it spreads, has remained something of a mystery to scientists.

A new study published Friday in the journal PLOS Computational Biology hopes to change that. In the study, researchers analyzed the spread of influenza in the US between 2002 and 2010. Then they combined medical claims data with census data on work commutes, as well as Department of Transportation data on domestic air travel to identify the probable origin and spread of eight separate epidemics.

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They found that seven of eight epidemics began in the South—a conclusion that contradicts the popular belief that flu epidemics prefer arid climates. (Why just one epidemic started north of Dallas, however, remains a mystery.)

"Every winter, influenza is imported into the United States from other countries, sparking a nationwide epidemic followed by a subsequent extinction during the summer months," says Vivek Charu, one of the study's lead researchers.

Charu and his team posit that some combination of climate and environmental factors—coupled with the immunity level of the southern population—could help explain the origins of the spread. Travel is the second variable: Southerners are more likely to be exposed to travelers from other countries who sustain their flu seasons through the summer months.

Air travel, however, is probably less to blame for the spread than we previously thought. It's local travel, Charu argues, that is the predominant mode of influenza transmission. (This finding aligns with previous research that shows air travel bans aren't an effective way to contain the spread of pathogens.)

"This study, along with prior modeling work," Charu says, "confirms that a ban on domestic air travel would likely have little effect in slowing down the spread of a new pandemic influenza virus in the US once it has already been introduced."

Kids, he says, could be another culprit: They're more likely to be infected, but also less mobile— therefore, they're more capable of transmitting the virus within a smaller population. That could be one reason why, Charu notes, that summer and holiday breaks from school also align with seasonal variations in the spread of influenza.