A study by researchers at Weill Cornell Medical College tested the bacteria in New York's subway system - an underground world that averages 5.5 million riders weekly, according to The New York Times - and found that half of the DNA recovered from surfaces was from a completely unknown source and only 0.2 percent matched the human genome.
The study was published in the biweekly journal, Cell Systems.
"People don't look at a subway pole and think, 'It's teeming with life,'" geneticist and lead study author Christopher E. Mason told The New York Times. "After this study, they may. But I want them to think of it the same way you'd look at a rain forest, and be almost in awe and wonder, effectively, that there are all these species present - and that you've been healthy all along."
The PathoMap is the project developed by Mason after he noticed his daughter interacting with other daycare toddlers by sharing toys that they each had - at one point - in their mouths.
"Despite finding traces of pathogenic microbes, their presence isn't substantial enough to pose a threat to human health," Mason said in a press release. "The presence of these microbes and the lack of reported medical cases is truly a testament to our body's immune system, and our innate ability to continuously adapt to our environment.
"PathoMap also establishes the first baseline data for an entire city, revealing that low-levels of pathogens are typical of this environment. While this is expected in rural environments, we've never seen these levels before in cities. We can now monitor for changes and potential threats to this balanced microbial ecosystem."
Kevin Ortiz, a spokesperson for Metropolitan Transportation Authority, did not seem as enthusiastic as the scientists did about the results that he called "deeply flawed."
"As the study clearly indicates, microbes were found at levels that pose absolutely no danger to human life and health," Ortiz told The New York Times.
Mason believes the data was presented responsibly. "For us to not report the fragments of anthrax and plague in the context of a full analysis would have been irresponsible," he told The New York Times. "Our findings indicate a normal, healthy microbiome, and we welcome others to review the publicly available data and run the same analysis."