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New Study Calls Subway Germs Mostly Harmless

6.29.16

A train on the Red Line of Boston's subway—one of three lines where Huttenhower's team collected data

Photograph by Adam E. Moreira/Wikipedia


A train on the Red Line of Boston's subway—one of three lines where Huttenhower's team collected data

Photograph by Adam E. Moreira/Wikipedia

Boston’s subway system is full of germs left behind by commuters on seats, poles, and touchscreens—but that may not be cause for concern, according to the results of a new study published this week in mSystems. The research was conducted by Curtis Huttenhower, associate professor of computational biology and bioinformatics, and his team at the Harvard T.H. Chan School of Public Health (SPH).

Huttenhower’s team collected their data using cotton swabs, on occupied, moving trains and at a number of stations across Boston’s transit network, from Newton to Cambridge. The work took place on three normal workdays in 2013, in cooperation with the Massachusetts Bay Transportation Authority (MBTA). They then analyzed the samples’ DNA to precisely determine the microbes they had found: overall, Huttenhower said, the collection of bugs they identified was very similar to the assortment of organisms found on a healthy person’s skin. What they encountered “looked like what you would normally carry around and what you might transfer from person to person by shaking somebody’s hand,” he reported: “bugs that clearly come from people, predominantly skin, with a little bit of typical oral microbes and other human-associated bugs mixed in, along with some environmental plant and soil microbes.” 

Most notable, perhaps, is what the scientists did not find: any sign of dangerous germs hiding on the T. “We specifically set out to check for things that might be pathogenic,” Huttenhower said, explaining that the researchers checked both for infectious bugs and for other possible threats, like pieces of DNA “that can make good bugs go bad” or spread resistance to antibiotics. Fortunately for subway riders, he said, “We didn’t really find anything like that.”

To analyze the results, Huttenhower and his colleagues used so-called big data techniques to separate their desired results from the statistical noise. “The analysis itself had to take into account teasing apart real signals from different kinds of contamination,” Huttenhower explained. Although weeding out contamination receives less public attention than some of the “sexier” aspects of information science, he added, it is nonetheless “a critical part of big data analysis.”

The next step for the researchers is to “develop a method to see if the microbes we find are alive or dead,” according to Tiffany Hsu, a graduate student in biostatistics and first author of the new study. “It’ll be important to know what exactly can grow out there in a subway environment.” She also said that scientists are continuing to swab subway systems around the world, through a consortium known as MetaSUB, hoping to learn more about how microbes become resistant to drugs and how their populations vary depending on geography. (The Harvard study looked for variations between the samples collected in different parts of the Boston area, but did not identify any geographical trends.) 

Boston commuters should still take common-sense precautions, but they can breathe easy, Hsu said. “If you’re normally healthy, I don’t think there’s much to be worried about,” she added. “Aside from general hand-washing, there’s not really much to be worried about on the T. I don’t think we need to be wiping down the seats before we sit on them or anything like that.”

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