The miracle of the dramatic drop in Dane Countyâ??s black infant mortality rate has become more of a mystery, as the rate shot up last year after years of surprising declines that received national attention. Health officials learned last month that the countyâ??s rate of black babies who die before their first birthdays, which dropped nearly 70 percent from 1990-2001 to 2002-2007, increased last year to slightly above the previous level. Researchers, who have been studying what seemed to be going right, also are looking at what apparently went wrong last year. The recession could be to blame, said Dr. Thomas Schlenker, director of the Madison-Dane County Health Department.