A young adult presenting with swelling of the parotid glands is most likely to have which of the following diseases?

The presentation of swelling of the parotid glands is characteristic of mumps, a viral infection caused by the mumps virus. This disease is well-known for causing parotitis, which is inflammation of the parotid glands, leading to noticeable swelling and discomfort. Mumps primarily affects the salivary glands and can be accompanied by other symptoms such as fever, headache, and muscle aches.

In contrast, measles is associated with respiratory symptoms and a distinctive rash rather than swelling of the parotid glands. Rubella, while also a viral infection, typically results in a mild fever, rash, and lymphadenopathy, but not parotitis. Congenital rubella syndrome pertains to a specific condition resulting from maternal infection during pregnancy and does not present primarily with parotid gland swelling.

Thus, the symptom of parotid gland swelling directly points toward mumps as the most likely diagnosis. Recognizing the specific clinical manifestations associated with these viral infections is crucial for accurate diagnosis and management.