CDC Deﬁnitions of Nosocomial Infections
Deﬁnitions of Nosocomial Infections
The ability of data collectors to deﬁne infections as nosocomial and identify their sites consistently is of paramount importance. Use of uniform deﬁnitions is critical if data from one hospital are to be compared with those of another hospital or with an aggregated database (such the NNIS system).1-3 The NNIS systemdeﬁnes a nosocomial infection as a localized or systemic condition 1) that results from adverse reaction to the presence of an infectious agent(s) or its toxin(s) and 2) that was not present or incubating at the time of admission to the hospital (7, and NNIS Manual, Section XIII, May 1994, unpublished). For most bacterial nosocomial infections, this means that the infection usually becomes evident 48hours (i.e., the typical incubation period) or more after admission. However, because the incubation period varies with the type of pathogen and to some extent with the patient’s underlying condition, each infection must be assessed individually for evidence that links it to the hospitalization. There are several other important principles upon which nosocomial infection deﬁnitions are based1.First, the information used to determine the presence and classiﬁcation of an infection should be a combination of clinical ﬁndings and results of laboratory and other tests. Clinical evidence is derived from direct observation of the infection site or review of other pertinent sources of data, such as the patient’s chart (detailed in a later section of this chapter). Laboratory evidence includesresults of cultures, antigen or antibody detection tests, or microscopic visualization. Supportive data are derived from other diagnostic studies, such as x-ray, ultrasound, computed tomography (CT) scan, magnetic resonance imaging (MRI), radiolabel scan, endoscopic procedure, biopsy, or needle aspiration. For infections whose clinical manifestations in neonates and infants are different from thosein older persons, speciﬁc criteria apply. Second, a physician’s or surgeon’s diagnosis of infection derived from direct observation during a surgical operation, endoscopic examination, or other diagnostic studies or from clinical judgment is an acceptable criterion for an infection, unless there is compelling evidence to the contrary (e.g., information written in the wrong patient’s record,presumptive diagnosis that was not substantiated by subsequent studies). For certain sites of infection, however, a physician’s clinical diagnosis in the absence of supportive data must be accompanied by initiation of appropriate antimicrobial therapy to satisfy the criterion. There are two special situations in which an infection is considered nosocomial: (a) infection that is acquired in the hospitalbut does not become evidence until after hospital discharge and (b) infection in a neonate that results from passage through the birth canal. There are two special situations in which an infection is not considered nosocomial: (a) infection that is associated with a complication or extension of infection already present on admission, unless a change in pathogen or symptoms strongly suggests theacquisition of a new infection, and (b) in an infant, an infection that is known or proved to have been acquired transplacentally (e.g., toxoplasmosis, rubella, cytomegalovirus, or syphilis) and becomes evident at or before 48 hours after birth. There are two conditions that are not infections: 1) colonization, which is the presence of microorganisms (on skin, mucous membranes, in open wounds, or inexcretions or secretions) that are not causing adverse clinical signs or symptoms, and 2) inﬂammation, which is a condition that results from tissue response to injury or stimulation by noninfectious agents, such as chemicals. The information that follows contains the criteria that comprise the deﬁnitions of nosocomial infections (NNIS Manual, Section XIII, May 1994, unpublished). It lists the...
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