The New York City subway system has been mapped according to bacteria and other microbes found in the network. Among the disease-causing organisms found were varieties responsible for dysentery and bubonic plague.

Weill Cornell Medical College researchers examined 466 open subway stations, finding genetic evidence of 15,152 different lifeforms, about half of which were bacteria. Most of the species were either unidentified, or known to be harmless to humans. However, 67 potentially dangerous species were detected during the microbial census.

Around 5.5 million people ride subways in New York City every day. Bacteria on hands, shoes, and clothing can then land on surfaces in the subway, and spread to other passengers.

A Pathomap, or pathogen map, of the rail network was created, to reveal which varieties of microorganisms might be found in various areas.

"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. These bacteria may even be helpful, since they can out-compete any dangerous bacteria," Christopher Mason from Weill Cornell's Department of Physiology and Biophysics said.

One of the strangest results from the study is the large number of species that could not be identified. This suggests that these lifeforms are unknown to biologists. New Yorkers - as well as people in other locations - are regularly exposed to these organisms, with unknown consequences. However, around 12 percent of the samples identified disease-causing organisms.

Anthrax was detected in two samples, and antibiotic-resistant bacteria were found in 27 percent of cases. Three samples tested positive for Yersinia pestis, the bacteria that causes bubonic plague. One bacteria common in mozzarella cheese was also detected in the NYC subway, as well as Shewanella frigidimarina, a marine organism native to Antarctica.

Bacteria was the source of 46.9 percent of the genetic material recorded in the study. Of these varieties, 57 percent have no known connection to disease, and 31 percent can cause illness in people with compromised immune systems. Most were commonly found throughout public areas.

"They are instead likely just the co-habitants of any shared urban infrastructure and city, but wider testing is needed to determine how common this is in other cities. Despite finding traces of pathogenic microbes, their presence isn't substantial enough to pose a threat to human health," Mason said.

Bubonic plague is believed to be the disease commonly known as the black death, which killed 25 million people in Europe during the 14th Century, between 30 and 60 percent of the continent's population at the time.

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