Unvaccinated 3‑year‑old child presents with fever, cough, coryza, conjunctivitis, Koplik spots and a maculopapular rash spreading from head to trunk—what is the diagnosis, how should it be confirmed, what isolation precautions are required, and what is the recommended management including vitamin A dosing and post‑exposure prophylaxis for contacts?

Measles: Diagnosis, Confirmation, Isolation, and Management

Diagnosis

This unvaccinated 3-year-old child has measles (rubeola), confirmed by the classic clinical presentation of fever, cough, coryza, conjunctivitis (the "three Cs"), Koplik spots, and a maculopapular rash spreading cephalocaudally from head to trunk. 1

Clinical Criteria for Diagnosis

The clinical case definition requires all three of the following 2:

• Generalized rash lasting ≥3 days
• Temperature ≥38.3°C (≥101°F)
• At least one of: cough, coryza, or conjunctivitis

Koplik spots on the buccal mucosa are pathognomonic when present and appear during the prodromal phase before the rash, making early diagnosis possible. 1, 3, 4

The rash characteristically begins on the face and behind the ears 2-4 days after fever onset, then spreads downward to the trunk and extremities in a cephalocaudal pattern. 1, 4

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Laboratory Confirmation

Serologic confirmation should be attempted for every suspected case, but reporting and isolation must not be delayed pending laboratory results. 2

Diagnostic Testing Approach

Collect blood for serologic testing during the first clinical encounter. 2 Laboratory criteria for confirmation include 2:

• Positive measles IgM antibody (most practical test)
• Significant rise in measles antibody level by any standard serologic assay
• Isolation of measles virus from a clinical specimen

Critical Timing Considerations

If measles IgM is not detected in serum obtained within the first 72 hours after rash onset, obtain another specimen because IgM may not be detectable with some assays until at least 72 hours after rash onset. 2 Measles IgM peaks approximately 10 days after rash onset and becomes undetectable 30-60 days later. 2

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Isolation Precautions

Immediate airborne isolation is mandatory—patients are contagious from 4 days before rash onset to 4 days after rash appears. 2, 1

Specific Isolation Requirements

• Implement airborne precautions immediately upon suspicion, before laboratory confirmation 1, 4
• Use negative pressure room when available 4
• Healthcare workers must use N95 respirators or equivalent 4
• Immediately report the case to local/state health department—measles is reportable in all states and requires urgent public health response 2, 1

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Management

Vitamin A Supplementation

All children with severe measles should receive vitamin A supplements, regardless of whether nutritional deficiency is suspected. 5

Dosing Schedule (WHO/AAP Recommendations)

For children with measles: 5

• Children <6 months: 50,000 IU orally once daily for 2 days
• Children 6-11 months: 100,000 IU orally once daily for 2 days
• Children ≥12 months: 200,000 IU orally once daily for 2 days

A third dose should be given 2-4 weeks later to children with clinical signs of vitamin A deficiency. 5

The landmark randomized controlled trial demonstrated that vitamin A treatment reduced hospital stay (10.6 vs 14.8 days), accelerated recovery from pneumonia (6.3 vs 12.4 days) and diarrhea (5.6 vs 8.5 days), reduced croup incidence, and cut mortality risk in half (relative risk 0.51). 5

Supportive Care

• Best supportive care with correction of dehydration and nutritional deficiencies 3
• Monitor closely for pneumonia—the most lethal complication and leading cause of measles-associated mortality 1, 6
• Treat secondary bacterial infections with appropriate antibiotics 1, 3
• Watch for encephalitis (occurs in approximately 1 per 1,000 cases), which typically presents during or shortly after acute illness 6

Fever Management Expectations

Fever typically lasts 5-7 days total: throughout the prodromal phase, peaking with rash onset, then gradually resolving over 2-3 days after rash appears. 6 Fever persisting beyond 2-3 days after rash onset should raise concern for bacterial superinfection or complications. 6

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Post-Exposure Prophylaxis for Contacts

Immediate Contact Assessment

Identify all contacts exposed during the contagious period (4 days before to 4 days after rash onset). 2 Evaluate immunity through vaccination records or serologic testing. 2

Prophylaxis Options

For susceptible contacts (unvaccinated or inadequately vaccinated):

• MMR vaccine within 72 hours of exposure is the preferred post-exposure prophylaxis for eligible individuals 2
• Immune globulin (IG) within 6 days of exposure for those with contraindications to live vaccine (infants <12 months, pregnant women, severely immunocompromised) 2
• Standard IG dose: 0.5 mL/kg intramuscularly (maximum 15 mL) 2

Healthcare workers who develop prodromal symptoms must be removed from patient contact immediately. 1

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Critical Pitfalls to Avoid

• Do not wait for the complete triad of fever, rash, and "three Cs" to develop before considering measles—only a minority present with all features at initial presentation 1
• Do not assume vaccination equals immunity—up to 5% of people who received a single vaccine dose have primary vaccine failure 2, 1
• Do not delay isolation or reporting while awaiting laboratory confirmation 2, 1
• Do not overlook measles in patients without rash—fewer than 50% have rash in the first 3 days, and some never develop rash 2