Germaphobes, you might want to stop reading right here. I'm about to confirm your every fear about riding public transportation. In a new study, researchers from Weill Cornell Medical College took a close look at the microbes present in the New York City subway system. And what they found might upset you.

According to the study, which was published in Cell Biology, NYC subway cars carry not only 5.5 million passengers each weekday, they also give a ride to hundreds of species of bacteria — some harmless, some not — as well as loads of DNA that does not match any organism currently known to science. Sound scary? Let's break it down a bit.

For the study, researchers fanned out across the subway system armed with cotton swabs that they used to collect DNA samples (in triplicate) from wooden benches, stairway handrails, seats, doors, poles and turnstiles. The purpose of the study was to create a pathogen map, dubbed a PathoMap, that could be used as baseline data to compare with similar studies in the future, track disease spread, or even mitigate bioterrorism threats.

And overall, their results were inert. The most commonly found organism (46.9 percent) was bacteria, and of the bacteria found, 57 percent had never been associated with any human disease. But 27 percent of the bacteria tested were from live, antibiotic-resistant samples. They also found that the diversity of the DNA sampled matched the unique diversity of NYC's boroughs. The Bronx was found to be the most diverse borough in terms of microbes, followed by Brooklyn, Manhattan, Queens and Staten Island. 

pathogen map of New York subway system

This graphic shows the relative amount of DNA found in the New York subway system form bacteria associated with the human body. (Graphic courtesy, Weill Cornell Medical College)

"We built maps that detail what organisms are present in each area of the city, creating a molecular portrait of the metropolis," says study co-author Dr. Cem Meydan, a postdoctoral associate at Weill Cornell Medical College. This is information that could prove useful when tracking the spread of a particular disease.

Researchers also found some more disturbing samples, including strands of DNA linked to bubonic plague and anthrax, although in both cases the DNA strands were found in low levels and were later determined not to be live samples.

Perhaps most interestingly, researchers found that about half of the DNA collected could not be identified — in other words, it did not match the DNA for any species currently listed in the databases for the National Center for Biotechnology Information or the Centers for Disease Control and Prevention. Which just goes to show how much scientists still have to learn about the living organisms that share our environment.

Researchers were quick to point out the NYC subways are still as safe to ride. "Our data show evidence that most bacteria in these densely populated, highly trafficked transit areas are neutral to human health, and much of it is commonly found on the skin or in the gastrointestinal tract," said Dr. Christopher E. Mason, an assistant professor in Weill Cornell's Department of Physiology and Biophysics. "These bacteria may even be helpful, since they can out-compete any dangerous bacteria."

Who knows? Maybe exposure to the subway's vast array of microbial life prevents, rather than causes disease. Or maybe you might want to do a better job of washing those hands when you get home from your weekday commute.

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From bacteria to bubonic plague: Study finds NYC subways are teeming with (microbial) life
It's intriguing — and a little scary — to know that the majority of DNA sampled did not match any living organism currently known to science.