Flu Spreads Faster Through Same-Gender Friendships

A study examining the spread of H1N1 in school classrooms showed that the ties that bind can also infect.

Parents often think of schools as cesspools of infection during flu season, but new research shows children’s social ties may have a larger impact on influenza's spread. In their study of a 2009 H1N1 outbreak among 370 schoolchildren in a rural Pennsylvanian town, researchers found that flu typically spreads 3 times faster among children of the same gender.

“There was evidence that boys were more likely to transmit influenza to other boys than to girls (and vice versa), which mimicked the observed assortative mixing among playmates,” researchers reported online in the Proceedings of the National Academy of Sciences.

At the same time, merely sitting next to or being the playmate of a child with influenza did not increase a child’s risk of contracting the illness. Likewise, early closure of schools due to flu did not slow transmission of the virus within the community. The researchers also found little evidence that school-aged children infected their parents.

One factor that significantly increased spread was the organization of schools into classes and grades. Transmission rates were much higher among classmates than they were between children in different grades, and the disease spread in 2 predominant waves: first from boys to boys, and then from girls to girls.

Although the study was relatively small, its findings help quantify the extent to which social networks shape disease outbreaks within structured communities. “Such detailed outbreak investigations are critically needed to improve our understanding of disease spread in human populations,” the authors concluded.

Lead author Simon Cauchemez, PhD, a research fellow at Imperial College London, said this data “could help us better understand whether and when it would be appropriate to close a school, or whether it might be better to close individual classes or grades.”

He collaborated with the Centers for Disease Control and Prevention and the Pennsylvania Department of Health to complete the research.

For other articles in this issue, see:

• Spike in Pharmacy Robberies Prompts NYT Exposé
• Study Reveals Inconsistencies in Black Box Warnings