Mobile sensors help track H1N1 transmission patterns

Last winter's outbreak of the H1N1 "swine flu" virus caused a lot of consternation and panic among the public, and left many an epidemiologist and physician scrambling for credible information to share with the concerned citizenry.

"Do you know how many contacts you have with infectious people on a daily basis? Do you know how many contacts you have with anybody on a daily basis?" Stanford University anthropologist James Holland Jones asks, according to the Stanford Report, a house organ. "Very often, those are the things we know the least about because they're the hardest to measure."

Jones and other researchers at the Palo Alto, Calif., school, used wireless sensors to track everyone who passed through an unnamed American high school one day last January, during the height of the H1N1 outbreak. Each student, teacher and staff member wore a credit card-size transmitter that tracked the person's location every 20 seconds.

This week in the Proceedings of the National Academy of Sciences, the Stanford team reported finding more than 760,000 incidents of two people passing within 10 feet of each other, approximately the maximum distance from which a disease can be transmitted by cough or sneeze. Each such interaction represented a chance to spread H1N1, or even the common cold.

"The enormous amount of interactions that occur in a single day is mind-blowing," says Marcel Salathé, a former Stanford postdoctoral researcher now on the faculty of the Penn State Center for Infectious Disease Dynamics.

What the researchers concluded is that if there were a limited amount of vaccine available, it doesn't matter if you inoculate the popular kids or the ones who keep to themselves unless you can be absolutely certain how people interact with each other.

"Almost nothing was better than the random strategy unless you measure who interacts with who and for how long in a typical day," Salathé tells the Stanford publication. "That flies in the face of what most people might think--that the super-popular kids with more connections than everyone else are more likely to spread more of the virus. But it doesn't matter if you're a teacher or a student or a staff member, or whether you're popular or not. Everyone's pretty much the same when it comes to transmission of the flu."

To learn more about this research:
- check out this story in the university-produced Stanford Report
- read the complete study in the Proceedings of the National Academy of Sciences (.pdf)