Principles Used in Definitions of Nosocomial Infections

First, information used to determine the presence and classification of an
infection involves various combinations of clinical findings and results of
laboratory and other diagnostic tests. Clinical evidence is derived from
direct observation of the patient or review of information in the patient's
chart or other ward or unit records. Laboratory evidence consists of
results of cultures, antigen- or antibody-detection tests, and microscopic
visualization methods. Supportive data are derived from other diagnostic
studies, such as results of x-ray studies, ultrasound examination,
computed tomography (CT) scan, magnetic resonance imaging,
radiolabel scans, endoscopic procedures, biopsies, and needle
aspiration. For infections whose clinical manifestation in neonates and
infants are different from those in older persons, specific criteria apply.

Second, a physician's or surgeon's diagnosis of infection derived from
direct observation during surgery, endoscopic examination, or other
diagnostic study, or based on clinical judgment, is an acceptable
criterion for an infection, unless there is compelling evidence to the
contrary.

Third, for an infection to be defined as nosocomial, there must be no
evidence that the infection was present or incubating at the time of
hospital admission.