We’re deep into flu season in the U.S. The federal Centers for Disease Control, which tracks the flu virus nationally, found a significant increase in flu-related hospitalizations and deaths in January.
I should admit to you that I was one of those patients. I came down with a cough mid-January that quickly turned into body aches and fever. Being pregnant, I went into the doctor for a check-up. They immediately sent me to the hospital where I tested positive for the flu. I was treated with IV fluids, fever-reducers and an antiviral medicine that has been shown to reduce the duration of the flu. Thankfully, I was much better within a week. While I was sick, I did find myself wondering more than once, “Where did I pick this virus up?” (My husband and son never got sick.)
So when I came across a new study in the Proceedings of the National Institutes of Science about how the flu spread, I was personally intrigued.
Researchers studied an outbreak of H1N1 flu virus at an elementary school in Pennsylvania in the spring 2009. They collected data in real time while the epidemic was going on, a unique method for studying the flu. In total, they collected information on 370 students from 295 households. Nearly 35 percent of the students and 15 percent of their family members came down with flu.
The interesting aspect of the study is that researchers collected data on exactly who got sick and when, plus information from seating charts, activities and social networks at the school. They then used statistical methods to trace the spread of the disease from one child to the next.
Their findings were surprising:
- Sitting next to a classmate with the flu did not significantly increase the risk of infection, but the social networks and the structure of classes certainly did.
- Transmission was 25 times as intensive among classmates as between children in different grades. Boys were more likely to catch the flu from other boys, and girls from other girls. From May 7 to 9, the illness spread mostly among boys. From May 10 to 13, it spread mostly among girls.
- Administrators closed the school from May 14 to 18, but there was no indication that this slowed transmission.
- Only 1 in 5 adults caught the illness from their own children.
The researchers did point out some limitations of the study. Survey data was reported by the main caregiver in each household and focused on symptoms only. And the study did not take into account how the flu spread outside of the school environment, at gatherings like play dates or sports practice.
But the study does provide a unique snapshot at how a virus can spread, revealing definite patterns of what the researchers call “back-and-forth waves of transmission” between the school, the community, and the households. It is one, detailed piece in the complex puzzle of understanding how disease spreads.
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