The most likely cause of delirium in hospitalized patients is which of the following?

• A. Infection
• B. Withdrawal from alcohol
• C. Stroke
• D. Parkinson disease

Answer: (A)

Delirium in hospitalized patients is an acute, fluctuating disturbance of attention and cognition, and infection is the most common precipitating factor in the hospital setting. Systemic infection—such as a urinary tract infection or pneumonia—triggers inflammatory responses and neurotransmitter imbalances (notably acetylcholine deficiency and altered dopamine and other pathways) that disrupt brain function, especially in older adults with limited reserve. Fever, metabolic stress, dehydration, and polypharmacy during illness further tip the balance toward delirium.

Alcohol withdrawal, stroke, and Parkinson disease can cause delirium, but they are less frequent primary triggers in the typical hospitalized population. Alcohol withdrawal can cause delirium tremens, but infections remain the more common precipitant overall. A stroke can cause acute confusion, but delirium due to infection occurs more commonly as a general cause in hospitalized patients. Parkinson disease is a chronic neurodegenerative condition; while it may contribute to delirium in the context of acute illness or medications, it is not the leading cause.

So, the most likely cause of delirium in hospitalized patients is infection.