What are the characteristics of measles?

Characteristics of Measles

Measles is characterized by a prodrome of fever ≥38.3°C (≥101°F), cough, coryza (runny nose), and conjunctivitis followed by a maculopapular rash that begins on the face and spreads downward to the trunk and extremities, with Koplik spots appearing during the prodrome as a pathognomonic finding. 1, 2

Clinical Presentation

Prodromal Phase

• High fever (≥38.3°C/≥101°F)
• Classic triad of "3 Cs":
  • Cough
  • Coryza (runny nose)
  • Conjunctivitis
• Koplik spots: pathognomonic white lesions on the buccal mucosa that appear during the prodrome 1, 3
• Duration: typically 2-4 days before rash onset

Exanthematous (Rash) Phase

• Maculopapular or morbilliform rash
• Characteristic progression:
  • Begins on the face
  • Spreads downward to trunk
  • Extends outward to extremities 1, 2
• Rash typically lasts ≥3 days 1, 2

Transmission and Contagiousness

• Highly contagious viral disease with R₀ of 15-20 4
• Transmission occurs primarily via respiratory aerosols/droplets 1, 5
• Contagious period: 4 days before rash appearance to 4 days after rash onset 1
• Virus can remain active on surfaces for several hours 1

Diagnosis

Clinical Case Definition

A clinical case of measles is defined as:

• Generalized rash lasting ≥3 days
• Temperature ≥38.3°C (≥101°F)
• At least one of: cough, coryza, or conjunctivitis 1, 2

Laboratory Confirmation

• Serologic testing:
  • Positive measles IgM antibody
  • Significant rise in measles antibody levels between acute and convalescent specimens
• Viral detection:
  • Isolation of measles virus from clinical specimen
  • Detection of viral RNA by RT-PCR 1, 2

Important timing note: IgM may not be detectable until at least 72 hours after rash onset with less sensitive assays 1

Complications

Complications occur in 10-40% of patients 3 and include:

• Respiratory: pneumonia, laryngotracheobronchitis
• Gastrointestinal: diarrhea, stomatitis
• Ear infections: otitis media
• Neurological (uncommon but serious):
  • Acute disseminated encephalomyelitis (ADEM)
  • Measles inclusion body encephalitis
  • Subacute sclerosing panencephalitis (SSPE) 6
• Higher risk in:
  • Young children
  • Pregnant women (risk of premature labor, spontaneous abortion)
  • Immunocompromised patients 2

Treatment

Treatment is primarily supportive:

• Vitamin A supplementation for all children with clinical measles:
  • 200,000 IU orally (100,000 IU for children <12 months)
  • Second dose on day 2 for complicated cases 2
• Antibiotics only for secondary bacterial infections
• Oral rehydration for diarrhea with dehydration 2
• No specific antiviral therapy is available 6

Prevention

• MMR (measles, mumps, rubella) vaccine:
  • First dose: 12-15 months of age
  • Second dose: 4-6 years of age 2
• Post-exposure prophylaxis options:
  • MMR vaccine within 72 hours of exposure
  • Immune globulin within 6 days of exposure for those with contraindications to vaccine 2
• Immediate reporting of suspected cases to public health authorities 1

Public Health Implications

• All suspected cases require immediate reporting to local health departments
• One confirmed case constitutes a public health emergency requiring prompt investigation and control measures 1
• Unvaccinated contacts should be excluded from outbreak settings for 21 days after the last case 1
• Vaccination coverage >95% is required to prevent endemic transmission 4

Despite the availability of an effective vaccine, measles remains a significant cause of morbidity and mortality worldwide, with over 100,000 deaths annually, primarily in developing countries 5, 6.