Aboard a No. 
local train in Manhattan, Weill Cornell researcher Christopher Mason patiently rubbed a nylon swab back and forth along a metal handrail, collecting DNA in an effort to identify the bacteria in the New York City subway.
In 18 months of scouring the entire system, he has found germs that can cause bubonic plague uptown, meningitis in midtown, stomach trouble in the financial district and antibiotic-resistant infections throughout the boroughs.
Frequently, he and his team also found bacteria that keep the city livable, by sopping up hazardous chemicals or digesting toxic waste. They could even track the trail of bacteria created by the city’s taste for pizza—identifying microbes associated with cheese and sausage at scores of subway stops.
The big-data project, the first genetic profile of a metropolitan transit system, is in many ways “a mirror of the people themselves who ride the subway,” said Dr. Mason, a geneticist at the Weill Cornell Medical College.
It is also a revealing glimpse into the future of public health.
Across the country, researchers are combining microbiology, genomics and population genetics on a massive scale to identify the micro-organisms in the buildings and confined spaces of entire cities.......Dr. Mason and his research team gathered DNA from turnstiles, ticket kiosks, railings and benches in a transit system shared by 5.5 million riders every day. They sequenced the genetic material they found at the subway’s 466 open stations—more than 10 billion fragments of biochemical code—and sorted it by supercomputer. They compared the results to genetic databases of known bacteria, viruses and other life-forms to identify these all-but-invisible fellow travelers.............
By Robert Lee Hotz
Feb. 5, 2015 1:07 p.m. ET
Want to read more? Source: http://www.wsj.com/articles/big-data-and-bacteria-mapping-the-new-york-subways-dna-1423159629
Want to found out your train station that has bacteria? Source: http://graphics.wsj.com/patho-map/?sel=stn_311