During which stage is measles considered most infectious?

Measles is most infectious during the coryzal stage, which occurs in the early phase of the illness. This stage is characterized by the onset of mild symptoms like a runny nose, cough, and fever, which often precede the more distinct rash. During this time, the virus is present in high amounts in respiratory secretions, and the person is capable of transmitting the virus to others, often before the rash appears. The infectious period begins several days before the rash, making this stage crucial in the spread of the disease.

In contrast, the febrile stage features a higher fever and malaise but is often still considered part of the contagious window, while the eruptive stage is when the characteristic rash appears, signaling a peak in visible symptoms. However, the peak infectivity is prior to or at the onset of the rash, affirming that the coryzal stage is key to understanding when measles spreads most easily among individuals. The convalescent stage occurs after the peak of the disease, indicating recovery and a significant reduction in viral load, which decreases infectiousness.