To conduct the study, MITRE researchers used a computational fluid dynamics model to investigate the extreme coughing and sneezing situations of seven passengers known as “super spreaders.” (Super spreaders cough and sneeze at a rate of 50 times per hour.) The software modeled the aircraft ventilation of a Boeing 767 airliner cabin, as many prior studies have done to determine the optimal sensor placement. But that does not tell you anything about the number of particles exhaled, says Hwang. The researchers found the fluid volume in saliva and divided it by the number of particles from a sneeze and a cough to get a distribution of particles. This, coupled with the data from the computational fluid dynamics model, allowed the researchers to compute the number of collectable bioparticles, says Hwang.
The researchers found that contamination traveled farther in sneezing than in coughing cases, and that particles from the two window-seat passengers entered the outlet vents quickly and were the least circulated in the cabin. In contrast, particles from the three passengers in the center row lingered and were not transported as effectively as particles exhaled from passengers in the two aisle seats of the aircraft’s two outside rows.
For the purposes of the study, the researchers assumed that they had approximately 90 minutes to detect a virus. That’s about the length of time that it takes to fly from Vancouver to San Francisco–a flight that often carries passengers who have just arrived from Asia.
Gendreau cautions that while the study did use sophisticated modeling techniques, the researchers did make assumptions about the super spreaders: “We don’t have a good idea of super spreaders’ characteristics.” However, the Center for Disease Control is putting a lot of money into addressing such knowledge gaps, and MITRE’s study is a nice start, says Gendreau.
The MITRE researchers also determined that to detect the presence of viruses, ultrasensitive biosensors are necessary. “The particles are small and dispersed, so you need detection down to the single particle level,” says Harkin. Currently, there are no commercial biosensors that can do that. Hwang and researchers at the University of California, San Diego, are building a novel surface plasmon polariton biosensor that has performed single molecule resolution in the laboratory. The sensor uses a plasmonic substrate with a gold surface that is perforated with nanometer-wide holes. A glycoprotein is attached to the gold surface inside each hole, and the researchers monitor the resonance of the photons that get transmitted through the gold nanohole. When a pathogen like H1N1 or H1N5 binds to the glycoprotein, the resonance changes. The work was featured in Nature earlier this year.