A patient with pneumonia for 5 days is admitted to the hospital in altered sensorium. He suddenly ceases to recognize the doctor and staff. He thinks that he is in jail and complains of scorpion attacking him. His probable diagnosis is -

Infection (like pneumonia) is one of the cause of delirium. Altered sensorium, disorientation to place (Patient thinks he is in jail) and person (not recognizing the doctor and staff), and hallucinations (scorpions attacking him) suggest the diagnosis of delirium.