Nosocomial infections in critical care units: causation and prevention.

Nosocomial infections reflect a dynamic interaction between host, agent, and environment. In the compromised host, the microbes most frequently associated with nosocomial infections in the ICU are bacteria that normally reside in or on body surfaces or in the environment. Infections occur when the host, compromised by the underlying disease, is exposed to a variety of diagnostic and therapeutic interventions that disrupt normal physical and chemical barriers and allow direct access to the internal milieu of the host. Efforts to prevent nosocomial infections in critical care units must take into consideration the interplay of all of these factors to be successful.