Being in close quarters during coast-to-coast airline travel can be challenging, but for Georgia Institute of Technology mathematics professor Howie Weiss it's the prime way to do detective work.
Weiss and his research team have been observing passengers' and flight attendants' every move as part of a Fly Healthy research study sponsored by Boeing, whose stated goal is to "understand the rates and routes of transmission of infectious diseases in an airplane cabin during flight and to find strategies to mitigate transmission."
Weiss, a AAAS Fellow, was given this opportunity to combine theoretical math with medical science when Boeing's chief aerospace physician reached out to him to lead the project. The biomathematical research, which is in its third year, also includes Georgia Tech, the Rollins School of Public Health at Emory University, and Delta Airlines.
The researchers are developing mathematical models to estimate how infectious diseases may spread during a flight by combining measured levels of pathogens, their estimated infectivity, and the many observed patterns of contact among those onboard.
"We took ten transcontinental research flights on which we had ten graduate student observers carefully chronicle the movements, behaviors, and close contacts of passengers and crew members," Weiss said.
The students were outfitted with a special iPad app that recorded the movements of passengers and crew in their assigned zone while the aircraft was above 10,000 feet. They specifically noted when two individuals were within a meter of each other--close enough contact to allow disease transmission.
According to Weiss, this transmission model, called a "dynamic network model," is akin to "relationships in high school. They change every day." The nodes of the model are the individuals on the plane, and any two nodes are connected by an edge at a given instant if the two individuals make contact.
For the microbial aspects of the data collection, one researcher operated pumps that sampled the cabin air, while another team gathered surface swabs from places every frequent traveler knows pathogens are likely be found, such as lavatory door handles, tray tables, and seat belt buckles. The air samples and surface swabs were analyzed for hundreds of different respiratory viruses and bacteria.
These data are being combined with other studies, such as an examination of an influenza outbreak among passengers stranded a few years ago on a commercial airliner. Weiss's team can then estimate the probability of flu and SARS transmission when a susceptible individual is in close contact with an infectious individual. The goal is to create strategies to lessen those encounters.
Weiss's high-flying research on disease transmission has taken him far from the world of pure mathematics where he earned his reputation for his work on dynamical systems and topology.
"At first I got interested in biomathematics to find new examples of dynamical systems and new mathematics. But after several years, I became more interested in the biology than the theoretical mathematics. My daughters call me a 'wannabe biologist,' " said Weiss.
"Mathematical models can significantly aid biologists and medical scientists in their investigations, and can even play a central role to help generate hypotheses, evaluate outcomes of experiments, and test plausibility of assumptions," he said.
While the math is generally straightforward, the human behavioral component of disease movement can be confounding. Such is the case, Weiss says, with parents who refuse to have their kids vaccinated.
"Measles is one of the world's most contagious infectious diseases. Measles epidemics can only be prevented by achieving a very high vaccination coverage. We have a highly effective vaccine, which protects against measles, mumps, and rubella. I strongly believe that schools must require vaccination of all children who are medically able to receive the vaccine. No personal belief or religious exemptions should be allowed," he said.
While diseases move swiftly in our globetrotting world, so does information, Weiss notes, particularly given the power of social media as a new force to gather and disseminate this time-sensitive data.
"I keep current on infectious disease outbreaks around the world using ProMED, (The Program for Monitoring Emerging Diseases) and CIDRAP (Center for Infectious Disease Research and Policy) on Twitter, which are edited by expert," he said, adding, "I also subscribe to some top experts in infectious diseases and public health."
Usually, Weiss says, vigorous reporting can have a substantial effect on reducing the impact of an outbreak, because an informed public will take precautions, from staying home, to canceling travel, to avoiding crowds.
But the modeling of disease transmission, or any other quickly changing system, is no simple task.
"Weather models are based on very well-established physical principles and equations, and we all know how unreliable weather forecasts can be, even for 24-hour prediction," observes Weiss.
"The theoretical foundation for disease transmission models is far less sound than weather prediction. Furthermore, human behavior, which needs to be inputted into the disease models, is usually quite difficult to predict accurately."