Beginning July 1, the three largest credit reporting agencies — Equifax, Experian and TransUnion — are changing the way medical debt affects people’s credit ratings. Medical debt has become pervasive, as health care and insurance costs continue to rise, while income has not kept up with inflation. About 23 million people in the United States — roughly 9% of the population — owe at least $250 in medical expenses, according to the Peterson-Kaiser Family Foundation Health System Tracker. Black people, women, people with complex medical issues, and those with low incomes are most likely to have me…