How dirty is San Francisco? An NBC Bay Area Investigation reveals a dangerous mix of drug needles, garbage, and feces throughout downtown San Francisco. The Investigative Unit surveyed 153 blocks of the city ‐ the more than 20-mile stretch includes popular tourist spots like Union Square and major hotel chains. The area ‐ bordered by Van Ness Avenue, Market Street, Post Street and Grant Avenue ‐ is also home to City Hall, schools, playgrounds, and a police station.

As the Investigative Unit photographed nearly a dozen hypodermic needles scattered across one block, a group of preschool students happened to walk by on their way to an afternoon field trip to city hall.

"We see poop, we see pee, we see needles, and we see trash," said teacher Adelita Orellana. "Sometimes they ask what is it, and that’s a conversation that’s a little difficult to have with a 2-year old, but we just let them know that those things are full of germs, that they are dangerous, and they should never be touched."