As SARS emerged in 2003, attention quickly turned to airplanes, the most likely source of international spread. At the time, the US Centers for Disease Control and Prevention (CDC) received passenger manifests, usually in hard copy, to notify people who had shared a flight with someone later diagnosed with the infection.
In the Internet age, that procedure was hardly ideal. "The paper management of data was problematic," says the CDC's Christie Reed, mainly because of the difficulty of sharing information with other health officials across the country. When the CDC's actions in response to SARS were later evaluated, "there was a recommendation that we develop a better, more rapid system to notify persons who may have had exposure," Reed says.
That's when CDC scientists began to work on eManifest, an in-house CDC database that imports electronic passenger data that the airlines give to the CDC, says Nancy Gallagher, a CDC contractor. For passengers that CDC determines may have been affected, eManifest "looks at the information that's provided - state, ZIP, area code - for their permanent information or their temporary information or their emergency contact information and it assigns them to a state," says Gallagher.
From there, passenger data are distributed to state or territory health departments via a secure network called the Epidemic Information Exchange (Epi-X) that is housed at the CDC. Approved state health officials subscribe to Epi-X and are notified by E-mail if a state resident may have been exposed to a pathogen. State health department employees then do their best to contact everyone on the list, says Karen Marienau of the CDC's Minneapolis Quarantine Station.
The program had its first test following a mumps outbreak in Iowa in December 2005. "Mumps had been almost completely wiped out in the US," Marienau says, "and so that's one of the reasons why we're trying to notify as many people as possible and trying to learn more about how it really is transmitted on airplanes."
As of April 25, the CDC had received reports of five Iowans and one Californian with mumps who flew on a total of 21 different commercial flights during the disease's contagious period (from three days before to nine days after symptom onset). From the first nine flights carrying a mumps-infected flyer, health officials have managed to contact 81% of potentially affected passengers, but contact information is not as good for some of the other flights, Marienau says, so those efforts may not be as successful.
Success usually depends on the type of contact information that the airlines have. "The airlines only have as accurate of information as the passengers provide," says Marienau. If passengers don't provide current phone numbers and addresses when they make reservations, "it can be extremely difficult to locate somebody and notify them."
The number of people who need to be notified depends on the pathogen, says Marienau. "There's really nothing that's been written or published about how easily mumps transmits or might transmit on airplanes." So, they use the measles recommendation: On a large plane, passengers in the same row, one row in front, or one row behind the index case are considered at risk. On small airplanes, they try to notify everyone.
So far, none of the passengers contacted has reported mumps symptoms, Marienau says. State health departments will contact everyone a second time, about 25 days after possible exposure, to ask again.
An efficient electronic system for notifying flyers potentially exposed to infectious disease will also require that airlines make some changes to their passenger data systems, says Gallagher. Even though airlines take electronic reservations, this doesn't mean they have those data in a format that can be easily queried and sent securely to the CDC, she says. Storing these data electronically "is a new format for them and it hasn't been standardized, so it's all new right now."