New York City's subway system is the dirtiest subway system in America.  

The people over at Travel Math decided to see just how dirty the subway systems in NYC, Washington D.C., Chicago, Boston, and San Francisco are taking 15 different samples from trains and studying the results. 

Unsurprisingly, NYC's subway system was the dirtiest of the five, with a staggering 2,000,030 colony-forming units (aka bacteria colonies) per-square-inch. 

What exactly does that number mean? 

Well, when you consider that the second dirtiest system is the Bay Area Rapid Transit system of the San Francisco Bay Area with 483 colony-forming units,  NYC's 2,000,030 CFU's seem pretty drastic. 

But why exactly is the NYC system so dirty? 

Considering the subway transports 2.8 billion people a year, and the other systems transport anywhere between 132 million to 271 million a year, it's almost inevitable that our system is going to be much dirtier than others. 

[anad]

So what kind of bacteria are lurking on the NYC subway poles and handles? 

Travel Math found that the bacteria on NYC's poles are primarily yeast or gram-negative rods. Yeast commonly lives on human skin and only rarely has an effect on humans. Gram-negative rods can cause respiratory and other infections.

Considering the amount of times we've encountered questionable bodily functions on the NYC subway, we're not surprised at the amount of bacteria living on the surfaces.

Check out This Study Shows 47% of NYC Commuters Wish They Had Germ-Killing Superpowers.

[via Travel Math] [Feature Image Courtesy New York Daily News]