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SEVERE ACUTE respiratory syndrome (SARS), which killed more than 700 people in 2003, was highly contagious and often spread on airplanes during flights. That prompted a recent study by the nonprofit MITRE Corporation, which looked at the ability of sensors to detect pathogens in exhaled particles in an airplane cabin.

The study examined particles exhaled in coughs and sneezes during a 90-minute flight. The researchers deduced that there are currently no sensors powerful enough to detect pathogens spread through air on a flight.

One of the reasons sensors can’t help right now is because there are so few particles to work with, according to lead biosensor scientist Grace Hwang, who headed up the research. Hwang says that after 90 minutes of collection, there averaged only about one collectible bacteria particle and fewer than one virus particle in the coughing scenario, and 300 bacteria particles and seven virus particles in the sneezing scenario.

“For that reason, I converged on the need for single particle detection,” says Hwang. “What that means is the sensor itself is so sensitive that one viral or bacterial particle can trigger the sensor and inform the user that a pathogen of concern has been detected.”

Hwang adds that most commercially available sensors that do not require any kind of secondary operation require more than a million particles before they can accurately identify a pathogen.

If an effective sensor were developed, it could be helpful in containing the spread of a disease, particularly between geographic areas. “We don’t want to just land this aircraft and have those people distribute to the four winds and then carry that exposure all over the place,” says Byron Jones, of the college of engineering at Kansas State University, who works with ACER (air cabin environment research), Federal Aviation Administration National Center of Excellence for Research in the Intermodal Transport Environment. “This would give you an ability when an airplane lands to have a quarantine process set up so that those passengers aren’t distributed to the general public.”

MITRE’s work highlights the difficulties in detecting the spread of disease through air on an airplane. In addition to the single particle issue, another challenge is that before any such sensor would ever be added to planes, it would have to generate an extremely low false-alarm rate. A false-alarm rate of less than one per million flights “is potentially acceptable,” says Hwang. That would require an extremely accurate sensor.

Hwang is currently working on a sensor that might be able to be used to detect single particles in the future. It uses a method called plasmonics, and it could be helpful in an aircraft situation, because it does not require a secondary operation to detect whether a pathogen is present. It could, therefore, provide relatively instant results.

The ability to have a sensor that could detect pathogens in the cabin air in a timely fashion is likely years away, says Hwang. However, there is plenty of work being done on technology that screens passengers before they board the plane, which could also prevent disease spread.

Flight attendants and airlines can do more as well, says Diana Fairechild, an airline cabin environmentalist and a former flight attendant.

Airlines should not recirculate their air (many newer Boeing airplanes recirculate about 50 percent of their air), says Fairechild, and they should not charge fees when sick passengers cancel their flights.