A 70 year old lady presents with fever for 3 days and confusion. There is no significant PMH (past medical history). What is the most probable diagnosis?

The key is A. Delirium. [Delirium is an acute confusional state and declined cognitive function which

involves changes in arousal (hyperactive, hypoactive or mixed), perceptual deficits, altered sleep-wake

cycle, and psychotic features such as hallucinations and delusions].