How should measles be diagnosed, isolated, treated, and prevented, including vitamin A dosing and post‑exposure prophylaxis for unvaccinated individuals?

Measles: Diagnosis, Isolation, Treatment, and Prevention

Diagnosis

Measles should be suspected in any patient with fever ≥38.3°C (101°F), generalized rash lasting ≥3 days, and at least one of the classic triad: cough, coryza (runny nose), or conjunctivitis. 1

Clinical Case Definition

• Generalized maculopapular rash lasting ≥3 days 1
• Fever ≥38.3°C (≥101°F) 1
• At least one of: cough, coryza, or conjunctivitis 1

Laboratory Confirmation

Obtain serum for measles IgM antibody testing during the first clinical encounter—do not delay reporting or implementing control measures while awaiting results. 1

• Measles IgM antibody (direct-capture IgM EIA method preferred for sensitivity and specificity) 1
• Timing matters: IgM may not be detectable until 72 hours after rash onset with less sensitive assays; if negative before 72 hours, repeat testing after 72 hours 1
• IgM remains detectable for at least 1 month after rash onset 1
• Alternative confirmation: Significant rise in antibody titer between acute (1-3 days after rash) and convalescent (2-4 weeks later) specimens 1
• Viral isolation: Collect urine or nasopharyngeal specimens as close to rash onset as possible for viral isolation and genetic characterization (useful for epidemiologic tracking, not for diagnosis) 1

Common pitfall: False-positive IgM results can occur with parvovirus infection (fifth disease), especially when using certain commercial ELISA assays—confirmatory testing with direct-capture IgM EIA should be considered for suspected cases without identified source or epidemiologic linkage. 1

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Isolation and Infection Control

Immediately place any patient with suspected measles in an airborne-infection isolation room (negative air-pressure) and have them wear a medical mask upon arrival at any healthcare facility. 1, 2

Isolation Requirements

• Isolation duration: At least 4 days after rash onset 1, 2
• Contagious period: 4 days before rash onset through 4 days after rash onset 1, 2, 3
• Room requirements: Negative air-pressure room; if unavailable, use private room with door closed 1, 2
• Patient masking: Medical mask immediately upon arrival 1, 2

Healthcare Worker Protection

All staff entering the room must wear N95 respirators (or equivalent) regardless of immunity status—surgical masks do not provide adequate protection against airborne measles. 1, 2, 4

• Only immune personnel should provide direct patient care when possible 1, 2
• HCP with measles must be excluded from work until ≥4 days after rash onset 1, 4
• Exposed susceptible HCP must be excluded from work from day 5 through day 21 after exposure 1, 2

Critical pitfall: The ~1% vaccine failure rate means even vaccinated HCP should use N95 respirators when caring for measles patients. 1, 4

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Treatment

Vitamin A Supplementation

All children with measles must receive vitamin A supplementation—this is the only evidence-based intervention proven to reduce measles mortality and should never be omitted. 2, 3, 5

Standard Dosing

• Age ≥12 months (including adults): 200,000 IU orally 2, 3
• Age <12 months: 100,000 IU orally 2, 3
• Do not give if vitamin A was received in the preceding month 2

Complicated Measles (pneumonia, otitis media, croup, severe diarrhea, neurological complications)

• Second dose of vitamin A on day 2 2, 3
• Two doses of 200,000 IU reduce overall mortality by 64% (RR 0.36; 95% CI 0.14-0.82) 5
• Pneumonia-specific mortality reduced by 67% (RR 0.33; 95% CI 0.08-0.92) 5, 6
• Greatest benefit in children <2 years: 82% mortality reduction (RR 0.18; 95% CI 0.03-0.61) 5, 6

Ocular Signs of Vitamin A Deficiency

• Extended regimen: Day 1, day 2, and 1-4 weeks later 2, 3
• Half-dose for infants <12 months 2

Evidence note: Single-dose vitamin A (200,000 IU) does not significantly reduce mortality (RR 0.77; 95% CI 0.34-1.78), but two doses do—this is why the two-dose regimen is critical for complicated cases. 5, 6

Supportive Care

• Nutritional support: Monitor nutritional status and enroll malnourished children in feeding programs 2, 3
• Hydration: Oral rehydration for diarrhea 2
• Antibiotics: Only for documented bacterial superinfections (e.g., pneumonia, otitis media) 2
• Avoid aspirin in children and adolescents due to Reye syndrome risk 3

Post-Infection Monitoring

Encephalitis characteristically develops approximately 10 days after initial infection—maintain vigilance during this critical window. 3

• Encephalitis risk: ~1 per 1,000 measles cases 3
• Monitor for: Seizures (beyond simple febrile seizures), altered mental status, focal neurological deficits 3
• Long-term risk: Subacute sclerosing panencephalitis (SSPE) occurs in 4-11 per 100,000 cases, highest risk in children infected before age 2 3

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Post-Exposure Prophylaxis

MMR Vaccine

Administer MMR vaccine within 72 hours of exposure to prevent or modify disease in susceptible contacts—this is effective even in previously vaccinated individuals due to the ~1% vaccine failure rate. 1, 2, 4

• Timing: Within 72 hours of exposure 1, 2, 4
• Benefit: Can prevent or modify disease even if too late for complete prevention 1
• Exposed HCP without immunity: Give first MMR dose immediately and exclude from work days 5-21 after exposure 1
• HCP with one documented dose: May remain at work and should receive second dose 1

Immune Globulin (IG)

Immune globulin is indicated for high-risk contacts who cannot receive MMR vaccine and must be given within 6 days of exposure. 1, 2

Standard Dosing

• Non-immunocompromised persons: 0.25 mL/kg IM (maximum 15 mL) 1, 2
• Pregnant women: 0.25 mL/kg IM (maximum 15 mL) 2, 3
• Immunocompromised patients: 0.5 mL/kg IM (maximum 15 mL) regardless of prior vaccination 2, 3

Monitoring After IG

• Extended observation: 28 days (instead of 21 days) because IG prolongs the incubation period 1, 2, 3
• Subsequent vaccination: Give measles vaccine 3 months after IG administration 3

Special consideration: IG is preferred over vaccine for infants <12 months who are household contacts, as they are at highest risk for complications and likely exposed >72 hours before diagnosis. 1

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Prevention and Outbreak Control

Routine Vaccination

• First dose: 12 months of age 2
• Second dose: 4 years of age (or 10-16 years for catch-up) 2
• Two documented doses constitute presumptive immunity regardless of subsequent serologic testing 2, 4

Outbreak Settings

During outbreaks, vaccinate or exclude all persons without acceptable evidence of immunity—do not wait for serologic screening results as this delays critical outbreak control. 1

Educational Settings

• Revaccinate or exclude: All students, siblings, and staff born during or after 1957 without documentation of two doses of MMR (≥28 days apart, first dose ≥12 months of age) 1
• Revaccinated persons: May return immediately 1
• Unvaccinated/exempted persons: Exclude until 21 days after rash onset in last case 1, 2

Healthcare Settings

• All HCP without two documented doses: Receive MMR immediately 1
• HCP born before 1957: Strongly consider MMR during outbreaks despite presumed immunity from natural infection 1
• Exposed susceptible HCP: Exclude from day 5 through day 21 after exposure (or day 5 after first exposure through day 21 after last exposure if multiple exposures) 1
• Exposed HCP who receive IG but not vaccine: Exclude from day 5 after first exposure through day 21 after last exposure 1

Infants During Outbreaks

• Age 6-11 months: May receive MMR (monovalent measles vaccine preferred) as outbreak control measure 1, 2
• Subsequent doses required: Revaccinate at 12-15 months and again before school entry 1, 2

Individuals with Three MMR Doses and Negative Serology

Persons with three documented MMR doses are considered immune regardless of negative or equivocal serologic results—antibody titers can wane without loss of immune memory, and no additional doses are needed. 4

• Do not revaccinate based solely on negative titers 4
• Manage as immune based on vaccination history 4
• Post-exposure: May still benefit from MMR within 72 hours of exposure 4
• Infection control: Must still use N95 respirators when caring for measles patients 4

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Key Pitfalls to Avoid

• Failure to isolate during pre-rash phase: Patients are contagious 4 days before rash appears—high index of suspicion is critical 2, 3
• Using surgical masks instead of N95 respirators: Surgical masks do not protect against airborne measles transmission 1, 2
• Omitting vitamin A: This eliminates the only proven mortality-reducing intervention 2, 3, 5
• Single-dose vitamin A in complicated cases: Two doses are required for mortality benefit 5, 6
• Relying on negative serology after vaccination: Two documented MMR doses confer immunity regardless of antibody titers 2, 4
• Delaying outbreak control for serologic screening: Rapid vaccination is essential; screening delays critical intervention 1
• Assuming immunity ends at day 10: Encephalitis characteristically develops around day 10—maintain vigilance 3