**1. Introduction**

188 Epidemiology Insights

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Delirium, also called as organic brain syndrome, acute brain syndrome, acute brain failure, acute confusional episode and reversible or masked dementia, as a concept, stretches back to the age of Hypocrates (Burns et al., 2004). Delirium is described as a condition characterized by a disturbance of consciousness with reduced ability to focus, sustain, or shift attention according to the Diagnostic and Statistical Classification of Mental Disorders, Fourth Edition, Text Revision (DSM-IV-TR) criteria (American Psychiatric Association, 2000). Also, delirium involves a change in cognition (such as memory deficit, disorientation, language disturbance) or the development of a perceptual disturbance that is not better accounted for by a preexisting, established, or evolving dementia (American Psychiatric Association, 2000). In addition to these, impairment in the brain's ability to integrate perceptions correctly, coupled with memory deficits and confusion may result in psychotic symptoms in delirium. Hallucinations (especially visual and tactile), delusions, paranoia, illusions, and bizarre behavior are the commonly encountered psychotic symptoms in delirium (Leigh, 2008).

Delirium is associated with longer hospital stay, poorer functional outcome, and cognitive decline in addition to an elevated morbidity and mortality. Despite these adverse outcomes, delirium recognition rates are low (12–43%) and its management remains inadequate in up to 80% of patients (Morrison et al., 2003). These findings suggest lack of preventive and screening activities, missed diagnoses, and inappropriate management of diagnosed delirium (Michaud et al., 2007).
