The fifteen, from worst to least-worst:
Houston
Newark
San Bernardino
Detroit
Jersey City
Bakersfield
San Antonio
Fresno
Oklahoma City
Yonkers (NY)
Shreveport
Manhattan
Birmingham
Ontario (CA)
Los Angeles
I admit I am surprised to see Ontario on the list. When I was in Toronto, Winnipeg, and Regina (granted over a decade ago) the streets and alleyways were clean--as in very clean. In Toronto, (1979) someone was filming a movie and had trashed the alley to make it look like an American alleyway, but the city crew came in and cleaned it up while they were on lunch break. I imagine that caused a bunch of problems with the background mess in the film...
My bad. CA is also an abbreviation for Canada, and I read it as such. California, I understand. Surprised San Francisco didn't get a nod, but reading the article, they didn't mention poop in the streets as a deciding factor.