A 7-year-old unvaccinated child presents with high fever, cough, coryza, and conjunctivitis for 4 days, followed by a maculopapular rash starting behind the ears and spreading downward. On oral examination, blue-white spots on buccal mucosa are seen. The family lives in a community with low measles vaccination coverage. Which statement about the infectivity period is MOST accurate?

• A Infectious from day 1 of rash until rash fades
• B Infectious only during the prodromal (pre-rash) phase
• C Infectious from 4 days before rash appearance to 4 days after rash onset ✓
• D Not infectious once Koplik spots appear

Explanation

Measles is one of the most contagious of all infectious diseases. The infectious period is from 4 days before the rash appears (late prodromal phase, when Koplik spots are present) to 4 days after the onset of rash. The peak viral shedding occurs during the prodromal phase, which is why measles spreads so rapidly in unvaccinated communities. Koplik spots are pathognomonic and appear 1–2 days before the rash, during the period of maximum contagiousness.

Reference: Ghai Essential Pediatrics, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.