A person infected with measles is contagious during which time window?

• A. Only during fever
• B. Only after the rash appears
• C. 5 days prior to rash appearance and 4 days after
• D. Only before fever begins

Answer: (C)

Measles spreads mainly through airborne droplets, and the virus is shed in the respiratory tract well before the rash appears. This means someone can be contagious during the prodromal period as well as after the rash develops. The best answer captures that full window: about five days before the rash shows up and about four days after the rash begins. This reflects the real-life pattern that transmission can occur before any visible signs and continues for several days once the rash is present.

Fever is part of the illness but is not the marker of contagiousness, and contagion is not limited to only before or only after the rash. So options that limit contagion to only before the fever or only after the rash miss the important point that infectiousness spans both the pre-rash and post-rash periods.