The hospital may have exposed the patients to the viruses, because

A VA hospital may have exposed more man 1300 vets to hepatitis and HIV. St Louis hospital has sent letters to those vets. The patients may have been exposed to the viruses through contaminated dental instruments.
    They were actually doing additional work in order to protect their kind of delicate instruments. Sometimes policies don’t always get followed, because people have very good intentions but the end result is the policy that was supposed to be followed wasn’t followed.
    The hospital has sent certifying notification letters to the affected patients. And Missouri Congressman Ross Connor is calling for a full investigation into what went wrong.