What's riding the New York City subway, other than millions of humans each week? Pizza crud, gut germs — and scores of mysterious, unidentified microscopic species, according to a new study from Weill Cornell Medical College.
The research, which mapped the fungi, bacteria, and viruses found on New York's mostly underground rail system, reveals the crowded, fascinating and gross ecosystem. While the subway microbiome isn't as contagious as you may think, the study found, it's still not a good idea to lick the handrail.
"It's really kind of a community … the ecosystem of what we carry with us," says Christopher Mason, an assistant professor in Weill Cornell's Department of Physiology and Biophysics.
The Weill Cornell researchers attempted to identify all 15,152 microbes for a PathoMap, which could be used to track infectious disease outbreaks. The project was inspired by Mason observing his 8-month-old daughter sharing toys in daycare. He wondered: What kind of microbes do tots share? Then, what microbes do the 5.5 million weekly riders of the subway swap?
Most of the 637 known bacteria, viral, fungal, and animal species are commonly found on humans and do not cause illness. They did find some surprises, such as a match to a Tasmanian devil, although that turned out to be a false positive — no need to worry about a carnivorous marsupial riding the subway.
"There is no reason to be alarmed."
The teams frequently found enough yeast to make some of the stations look like a microbrewery.
"Parts of the subway look like people eating pizza," he says. "[We] see what people are eating in the subway."
Not surprising, they found a lot of gut bacteria.
"It might mean that people aren't washing their hands enough," he says. "It is a gentle reminder to wash your hands."
Only 12 percent of bacteria sampled can cause disease and about half of the DNA collected couldn't be linked to known pathogens. While many of the microbes remain mysterious, Mason says not to worry.
Some of the unknown microbes can only live on a railing or a plastic seat. When researchers try to cultivate them in the lab, they die. Mason knows they're safe for humans because we live with them daily and they haven't caused a new illness.
"The majority of the things there are harmless," he says.
The researchers did discover what seemed like some old, deadly microbes, anthrax (Bacillus anthracis) and Bubonic plague (Yersinia pestis). But, they found no evidence the samples were alive. Finding these microbes helps researchers understand what normal looks like as compared to an outbreak.
"There is no reason to be alarmed," he says.
The tests only looked at DNA, not RNA, so the team didn't identify many cold-causing viruses (which doesn't mean they're not there).
Mason's message to the millions of daily riders: The subway remains safe.
"The air in the subway is not very different than the air outside so it is no more dangerous than the air on the street," he says. "[It's] very much the same as a car seat, lunch table … and in no way represents a higher risk."