Without proper precautions, health care workers can easily pass micro-organisms to patients. In Michigan, 16 Pseudomonas infections were traced back to a nurse with a severe fungal infection under a fingernail; organisms from infectious cosmetics had colonized the wound. In California, seven patients contracted Serratia infections and one died apparently due to a Serratia colony on the artificial nails of a scrub nurse. Because workers can be such potent vectors for microorganisms, it's critical that they understand the principles that will help prevent being the source of a nosocomial outbreak. Here is an overview.