If you or your child came down with influenza during the H1N1, or swine flu, outbreak in 2009, it may not have happened the way you thought it did.
A new study of a 2009 epidemic at a school in Pennsylvania has found that children most likely did not catch it by sitting near an infected classmate, and that adults who got sick were probably not infected by their own children.
Closing the school after the epidemic was under way did little to slow the rate of transmission, the study found, and the most common way the disease spread was a through child’s network of friends.
Researchers learned all this when they studied an outbreak of H1N1 at an elementary school in a semirural community in spring 2009. They collected data in real time, while the epidemic was going on.
With this information on exactly who got sick and when, plus data on seating charts, activities and social networks, they were able to use statistical techniques to trace the spread of the disease from one victim to the next. Their report appears online in the Proceedings of the National Academy of Sciences.
The scientists collected data on 370 students from 295 households. Almost 35 percent of the students and more than 15 percent of their household contacts came down with flu. The most detailed information was gathered from fourth-graders, the group most affected by the outbreak.
The class and grade structure had a significant effect on transmission rates. Transmission was 25 times as intensive among classmates as between children in different grades. And yet sitting next to a student who was infected did not increase the chances of catching flu.
Social networks were apparently a more significant means of transmission than seating arrangements. Students were four times as likely to play with children of the same sex as with those of the opposite sex, and following this pattern, boys were more likely to catch the flu from other boys, and girls from other girls.