What symptom is characteristic of Measles?

The presence of Koplik's spots is a hallmark symptom of measles, making it the defining characteristic of this viral infection. These spots are small, white lesions that appear on the mucous membranes inside the mouth, typically a few days before the measles rash develops. They serve as a unique clinical feature, helping healthcare providers distinguish measles from other viral illnesses.

Koplik's spots are usually located on the buccal mucosa, opposite the molars, and are often described as looking like grains of sand surrounded by a red halo. Their appearance is a critical indicator for diagnosis, especially since measles is highly contagious and poses significant health risks.

In comparison, while a red-pink rash can occur with measles, it is more general and not exclusive to this disease. Fluid-filled lesions are characteristic of other viral infections, such as chickenpox, and swollen lymph nodes can occur with a variety of infections, not specifically measles. Therefore, the presence of Koplik's spots is a key differentiator in the clinical diagnosis of measles.