Fungi most often infect immuno-compromised patients or vulnerable people with a weakend immune system.
Due to it's ability to survive on artificial surfaces and resist dessication, it can remain and possibly infect new patients for some time.
With multiple breakdowns in such procedures, officials feared that some contaminated blood would be sent out, infecting unsuspecting patients.
But those four days left me with a realistic view of what infected patients often face.
In particular, it seemed unlikely that the two women could have infected other patients without becoming infected themselves:
Health care workers have said they fear dangerous side effects, or that they could accidentally infect patients or others with the vaccinia virus.
The treatment involved infecting patients with malaria which caused a high fever meant to kill the spirochetes which caused the disease.
But there are fears the cancer-derived cells could cause cancer and that cells from pigs could infect patients with animal viruses.
Doctors can infect patients if they fail to wash their hands and clean stethoscopes and blood pressure cuffs after treating infected people.
No other cases of health-care providers infecting patients are known.