Studies of delirium in general medical populations have used criteria for delirium different from current DSM-III or DSM-IIIR criteria of the American Psychiatric Association, or have used DSM-III or DSM-IIIR criteria without operationalizing the components of these criteria. Therefore this prospective study was conducted to establish an approach to operationalizing DSM-III criteria and to determine the incidence and prevalence of delirium. Two hundred thirty-five consecutive subjects age 70 and over admitted to general medicine underwent daily standardized screening. Patients with low scores on screening tests or clinical evidence suggestive of any psychiatric disorder and controls were seen by a psychiatrist, who determined whether delirium was present by applying explicit operational definitions to each component of the DSM-III criteria for delirium. We conclude that the syndrome of delirium as defined by the American Psychiatric Association is prevalent on admission among elderly on general medical services, but the number of cases developing in the hospital is much less than often stated in the literature.
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