Acute illness refers to a sudden onset of symptoms that are typically severe in nature and have a relatively short duration. These illnesses can manifest rapidly and often require immediate attention and intervention. Unlike chronic conditions, which persist over an extended period, acute illnesses are characterized by their sudden and intense nature.

Common examples of acute illnesses include respiratory infections like the flu or common cold, gastrointestinal issues such as food poisoning, injuries like sprains or fractures, and infections like urinary tract infections. Acute illnesses can affect various organ systems and can range from mild to severe.