A 6-year-old child develops high fever followed by a maculopapular rash starting on the face. Measles is suspected. Which combination of samples and timing gives the highest diagnostic yield?

• A Serum measles IgG alone, collected on the first day of fever
• B Paired acute and convalescent sera for IgG, collected immediately
• C Urine culture for measles virus, collected after 7 days of rash
• D Serum measles IgM plus throat or nasopharyngeal swab for RT-PCR, collected within 3 days of rash onset ✓

Explanation

Measles IgM becomes detectable around the time of rash onset and persists for about a month, making a single acute serum diagnostic. Virus is shed in respiratory secretions and urine most abundantly just before and up to 3 to 4 days after rash onset, so RT-PCR on a throat or nasopharyngeal swab taken early has high yield. IgG alone on day one cannot distinguish acute from past infection, and waiting 7 days misses peak viral shedding.

Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.