Whether it's hopping on a city bus or hailing a taxi, public transportation has the reputation of being a bacteria hotbed. But are all cities equally grimy?

Jeff Rossen and the Rossen Reports team used a bacteria meter to test public transportation systems across New York City, Los Angeles and Chicago to see how dirty they really are. Health experts say anything over 100 is a fail.

Are buses cleaner than subways? What about taxis? Let's check out the results.

New York City

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The MTA bus, the subway and the good old yellow cab. New York isn't known for its cleanliness, but is its grimy rep deserved?

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The city didn't get off to a great start; the bus handle the team tested had nearly double the amount of normal bacteria. But the Big Apple redeemed itself in the taxi test.

Jeff Rossen tests germ levels in public areas of three major cities. TODAY

That sample had a bacteria level under the 100-point threshold.

But the most surprising win came from the New York City subway. With a reading of 31, the subway proved remarkably clean!

Los Angeles

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The metro in Los Angeles was about as germy as a New York bus. And the swab came away with visible dirt, which was extra unsettling.

The above ground transportation wasn't much better. A bus pole the team swabbed had 259 points — over 150 more than the threshold. And the cab's credit card machine was even worse.

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Chicago

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The Midwestern city boasts about its relative cleanliness, so it should be able to pass the test, right? Wrong.

The CTA bus in Chicago clocked in at 730 — more than seven times the recommended threshold. But it didn't stop there; the taxi in Chicago came back with a score of 909. That's more than 800 points above the limit.

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Those scores are bad, but the test run on the Chicago L train was the worst Jeff Rossen has ever seen, coming back with a result of 4,032. That's over 40 times the acceptable amount of bacteria. Yikes!

Sorry, Chicago, out of the surfaces tested, yours were the dirtiest of all.

NBC Medical contributor Dr. John Torres warned that exposure to this bacteria isn't as harmless as we might assume.

"It's simple how fast it can happen. You touch the pole, you wipe your nose, you wipe your eye, you don't even think about it, bam, you're sick."