LOS ANGELES -- The city of Los Angeles is violating the county health code in its Skid Row area by allowing the nation's densest population of homeless people to live on streets infested with rats, human excrement and used hypodermic needles, the Los Angeles County Department of Public Health has found.An extensive agency inspection of the downtown district found nearly 90 rats' nests, mostly around street planters, people living in about 60 tents on sidewalks – some with animals – and 90 piles of human waste.