The city's Medical Officer of Health is wondering if the Health Unit's needle exchange program will be overwhelmed as Oxycontin addicts move to other drugs. Dr. David Williams says if the program can't meet the anticipated demand, it could result in the outbreak of infectious diseases such as H.I.V. Aids, Hepatitis C and other sicknesses. He says that could be disastrous for some communities if they can't get a grip on a sudden mass use of illicit drugs that they have no control over.