What is the most likely diagnosis in a previously healthy 20‑year‑old male college sophomore presenting with cough, high fever, rhinorrhea, conjunctivitis, and an erythematous maculopapular rash that began at the hairline and spread downward to the trunk and extremities?

Measles (Rubeola)

The most likely diagnosis is measles (rubeola), a highly contagious viral illness characterized by the classic triad of cough, coryza (runny nose), and conjunctivitis, followed by high fever and a pathognomonic erythematous maculopapular rash that begins at the hairline and spreads cephalocaudally to the trunk and extremities. 1

Clinical Presentation Confirms Measles

The patient's presentation is textbook for measles:

• The prodromal triad of cough, coryza, and conjunctivitis is pathognomonic for measles and distinguishes it from other viral exanthems. 1
• High fever (typically 101-104°F) with acute onset is characteristic of measles, unlike the milder fevers seen in rubella (>99.0°F). 1
• The erythematous maculopapular rash appearing at the hairline and spreading downward in a cephalocaudal distribution (face → trunk → extremities) is the hallmark presentation of measles. 1, 2, 3
• The rash typically appears 2-4 days after fever onset and becomes more confluent as it spreads. 1, 3

Key Distinguishing Features from Other Diagnoses

Measles is distinguished from rubella by prominent respiratory symptoms (cough, coryza), conjunctivitis, higher fever, and the absence of arthralgia/arthritis or prominent lymphadenopathy. 1

• Rubella presents with milder constitutional symptoms, lower fever threshold, and typically includes arthralgia or lymphadenopathy. 1, 4
• Rocky Mountain Spotted Fever would begin with small blanching macules on ankles/wrists 2-4 days after fever, spreading centripetally to involve palms and soles—not starting at the hairline. 1, 5
• Roseola (HHV-6) occurs primarily in infants and presents with rash appearing precisely when fever breaks, not during ongoing fever. 6

Immediate Management Priorities

Immediate airborne isolation is mandatory, as measles patients are contagious from 4 days before rash onset to 4 days after rash onset. 1

• Measles is a reportable disease requiring urgent notification to public health authorities. 1
• Remove the patient from contact with other individuals immediately to prevent transmission in the college setting. 1

Critical Complications Requiring Monitoring

Pneumonia is the most lethal complication and accounts for most measles-associated morbidity and mortality. 1

• Other serious complications include encephalitis and secondary bacterial infections. 1, 2
• Complications occur in 10-40% of patients and require close monitoring. 3

Treatment Approach

Treatment is primarily supportive care, as there is no specific antiviral cure for measles. 7

• Vitamin A supplementation is essential in management per CDC recommendations. 1
• Patients who are pregnant, immunocompromised, or unvaccinated may require measles vaccine, intravenous immunoglobulin, or ribavirin in severe cases. 1

Common Pitfalls to Avoid

• Up to 5% of people who received a single vaccine dose have primary vaccine failure—do not assume vaccination equals immunity. 1
• The college setting creates high risk for outbreak given close contact among young adults who may have incomplete vaccination. 2, 7
• Koplik spots (small white spots on buccal mucosa) may appear during the prodromal phase and are pathognomonic when present, though they are not always visible. 1, 3
• Young clinicians may have never seen a case of measles and should maintain high clinical suspicion given recent resurgence in the United States. 2, 7