[cfghcrtyd]

Dude:

  colonoscopies with dirty equipment 
  led to a rash of hepatitis and HIV

...pretty much in the worst way imaginable.

Following the links the article provides:

  Army veteran Thomas Mayo got a colonoscopy 
  after the VA insisted on it - only to learn 
  it may have left him with a chronic disease.

  6 veterans who took the follow-up blood checks 
  tested positive for HIV, 34 tested positive for 
  hepatitis C and 13 tested positive for hepatitis B. 
  But there is no way to prove [blah blah blah], and 
  some [roll their eyes, accuse the victims of lying 
  and accept paychecks to play devil's advocate, 
  claiming maybe] the infections probably already 
  existed.

You pretty much have to figure anyone that cares enough about their health to subject themselves to an elective colonoscopy, probably has a firm awareness of their HIV/hepatitis status, before hand, including the patient zero carrying the source of the disease in each case. There are likely medical records capable of proving which patients were the infectious patient zeroes, and which contracted the disease as a result of the malpractice, even if those identities are never made public due to privacy law.