What are the diagnostic criteria and management options for measles?

Measles Diagnosis and Management

Diagnose measles clinically with fever ≥38.3°C (101°F), generalized rash ≥3 days, plus cough, coryza, or conjunctivitis, and confirm with serum measles IgM antibody testing collected during the first clinical encounter. 1, 2

Diagnostic Criteria

Clinical Case Definition

A clinical case of measles requires ALL of the following: 1

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

The rash classically begins on the face and spreads cephalocaudally (head to toe), becoming more confluent as it progresses. 3 Koplik spots (pathognomonic enanthem on buccal mucosa) may appear before the rash, providing early diagnostic opportunity. 3, 4

Laboratory Confirmation

Primary diagnostic test: Serum measles-specific IgM antibody using direct-capture IgM EIA method. 1, 2 This is the most sensitive and specific test when collected at the time of rash onset. 2

Critical timing considerations for IgM testing: 1, 2

• Collect blood during the first clinical encounter with suspected measles
• IgM may not be detectable in the first 72 hours after rash onset with some assays
• If negative within first 72 hours, obtain a second specimen ≥72 hours after rash onset
• IgM peaks approximately 10 days after rash onset
• IgM remains detectable for at least 1 month after rash onset
• Seropositivity rate is 92-100% when collected 6-14 days after symptom onset 2

Alternative laboratory criteria: 1

• Significant rise in measles antibody level between acute (1-3 days after rash) and convalescent (2-4 weeks later) serum specimens
• Isolation of measles virus from clinical specimen (urine or nasopharyngeal mucus)

Case Classification

Suspected case: Any febrile illness accompanied by rash. 1

Probable case: 1

• Meets clinical case definition AND
• Not epidemiologically linked to a confirmed case AND
• Has not been serologically/virologically tested or has noncontributory results

Confirmed case: 1

• Meets laboratory criteria (positive IgM, significant antibody rise, or virus isolation) OR
• Meets clinical case definition AND is epidemiologically linked to a confirmed case

Important Diagnostic Pitfalls

False-positive IgM results: 1, 2

• Can occur with parvovirus infection (fifth disease), other viral infections, or rheumatoid factor positivity
• Consider confirmatory testing with direct-capture IgM EIA when IgM is detected in a patient with no identified source of infection and no epidemiologic linkage

False-negative results: 2

• Occur if specimen collected too early (within first 72 hours of rash onset)
• Always obtain second specimen if clinical suspicion remains high

Clinical misdiagnosis: 5

• In one study, among children meeting clinical case definition, only 72% were IgM-positive for measles; 23% had rubella instead
• Laboratory confirmation is essential, particularly when vaccine effectiveness is questioned

Management

Supportive Care and Vitamin A Supplementation

Vitamin A is critical for all children with clinical measles: 6

• Children ≥12 months: 200,000 IU orally on day 1
• Children <12 months: 100,000 IU orally on day 1
• For complicated measles: Administer second dose on day 2 (same dosage)
• Vitamin A deficiency increases measles severity and mortality 6

Treatment of Complications

Bacterial superinfections: Treat with appropriate antibiotics 6, 3

Diarrhea: Oral rehydration therapy 6

Acute lower respiratory infections: Standard antibiotic treatment 6

Nutritional monitoring: Enroll in feeding program if indicated 6

Complications occur in 10-40% of patients, with pneumonia being one of the most lethal. 3, 4

Post-Exposure Prophylaxis

Measles vaccine: May provide protection if administered within 3 days of exposure 6

Immune globulin (IG) for persons with contraindications to vaccination: 6

• Standard dose: 0.25 mL/kg body weight (maximum 15 mL) as soon as possible after exposure
• Immunocompromised persons: 0.5 mL/kg body weight (maximum 15 mL)

Public Health Response

Immediate reporting is mandatory: 1, 2

• Report suspected and known cases immediately to local or state health department
• One confirmed case is an urgent public health situation requiring rapid investigation
• Do not delay reporting, investigation, or control activities pending laboratory results 1

Outbreak control measures: 1

• Vaccinate or exclude susceptible persons (those without acceptable evidence of immunity) from outbreak settings
• Persons exempted from vaccination should be excluded until 21 days after rash onset in last case
• Mass revaccination of entire communities is generally not necessary