Look at Chicago as a whole and it appears that lead poisoning is an epidemic from the history books. About 4 percent of children age 5 or younger who were tested in 2013 had alarming levels of the toxic metal in their bodies, compared with 68 percent of those tested in 1995. But while the problem has been largely eliminated in many parts of the city, the rate of lead poisoning is up to six times higher than the city average in some pockets of poor, predominantly African-American neighborhoods.