What microbes are lurking in the Boston subway system? A team of scientists armed with sterile cotton swabs and a bit of soap rode the Red, Orange and Green lines of the T to find out.
What they discovered surprised them.
It turns out that the slick metal poles and well-worn hand grips used by hundreds of thousands of riders each day are not hotbeds of pathogenic bugs as the researchers originally suspected.
Instead, they say the microbes on most of the sampled surfaces — including subway seats, touch screens and the walls of indoor and outdoor ticketing machines — look a lot like what you'd find on healthy human skin.
"From what we found, the bugs you encounter riding the T is not any worse than what you would expect from shaking someone's hand," said Curtis Huttenhower, a computational biologist at Harvard T.H. Chan School of Public Health in Boston. "Sure, a lot of microbes are involved, but it's nothing to worry about."
Huttenhower is the senior author of a paper published Tuesday in mSystems, the American Society for Microbiology's journal, that describes the findings.
His group also detected a smattering of microbes that usually live in our mouths on the poles and hand grips (about sneeze and cough level), as well as some vaginal microbes on the seats. But don't freak out: The authors said those can be transferred through clothing.
The researchers weren't specifically looking for the types of bugs that make us sick, but they did check for obvious pathogens.
"Our conclusion is that even though the subway can seem like a 'dirty' environment, it's not strikingly different from a conference room at work," Huttenhower said.
The study is part of an effort financed by the Alfred P. Sloan Foundation to better understand what microbes are living in built environments like shopping malls, office buildings, transit systems and even our homes.
The microbes in, on and around us have evolved to live in natural environments such as in soil, on plants and in our guts, mouths and skin. But what happens when those microscopic bugs land on an electronic touch screen or a vinyl subway seat or a piece of drywall?
Do they live? Do they eat? Do they multiply? Do they die?
"That is still a big open question," Huttenhower said. "And it is a difficult thing to measure."
So far, there have been only two other studies that looked at microbial communities in subway systems. One was conducted in New York, the other in Tokyo.
The authors of the New York study originally reported the presence of scary-sounding pathogens in the subway system, including traces of plague and anthrax, but those findings later were revised.
Because of the confusion around the New York City subway study, Huttenhower and his team decided to take their time with their study of the Boston subway system.
They swabbed 73 surfaces on trains and in stations in the fall and spring of 2013. The samples were brought back to the lab, where they were ground up so that the authors could see what DNA was present in each swab.
Huttenhower said the group deliberately avoided swabbing during the winter flu season and in the summer when the weather is hot and sticky in order to get a baseline measurement of microbes on the Boston T.
In the future, it is possible that researchers could keep tabs on the microbial composition of subway surfaces and use it as a way to tell whether flu symptoms are on the rise, he said.
"If we know what the baseline microbial profile looks like, then a change in that profile, or the sudden detection of a pathogen could provide an early notification that something is going on," he said.
The group's next project is to determine which of the microbes identified in the study were alive when they were collected, as well as how they might be surviving on the subway.
"If you are an organism that was designed to live on or in people, what do you do when you get dropped on a vinyl seat or a hand grip?" Huttenhower said.
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