What is measles?

What is Measles

Measles is a highly contagious viral disease caused by measles virus (a morbillivirus of the Paramyxoviridae family) that presents with a characteristic prodrome of fever, cough, coryza (runny nose), and conjunctivitis, followed by a maculopapular rash that begins on the face and spreads downward to the trunk and extremities. 1

Causative Agent and Transmission

• Measles virus is a strictly human pathogen with no animal reservoirs, transmitted by aerosols through direct human-to-human contact. 2, 3
• The virus is extraordinarily contagious, making it one of the most transmissible infectious diseases. 4, 2
• Patients are infectious from 4 days before rash onset through 4 days after rash appears. 4, 1

Clinical Presentation

Incubation and Prodrome

• The incubation period averages 10-12 days from exposure to prodrome onset and approximately 14 days from exposure to rash (range: 7-18 days). 1
• The prodromal phase features fever ≥38.3°C accompanied by the "three C's": cough, coryza, and conjunctivitis. 1, 5
• Koplik spots—small white spots on a red background inside the mouth—appear during the prodrome and are pathognomonic for measles. 4, 1

Rash Characteristics

• The maculopapular or morbilliform rash classically begins on the face and spreads cephalocaudally (downward) to the trunk and out to the extremities, becoming more confluent as it progresses. 4, 5
• The rash typically lasts ≥3 days. 1

Complications and Mortality

Common Complications

• Diarrhea is the most frequent complication, followed by otitis media (middle ear infection) and bronchopneumonia. 4, 1
• Complications occur in 10-40% of patients. 5
• Other complications include laryngotracheobronchitis (croup), stomatitis, and dehydration. 3

Serious Neurological Complications

• Acute encephalitis occurs in approximately 1 per 1,000 measles cases and is a leading cause of measles-related death, often resulting in permanent brain damage. 1, 6
• Subacute sclerosing panencephalitis (SSPE) is a rare but invariably fatal late complication that can appear years after the initial infection; widespread vaccination has essentially eliminated SSPE in countries with high vaccine coverage. 1, 6
• Measles inclusion body encephalitis and acute disseminated encephalomyelitis are other uncommon but serious neurological sequelae. 3

Mortality Rates

• In the United States and other developed countries, the case fatality rate is 0.1-0.4% (1-2 deaths per 1,000 cases). 1, 6
• In resource-limited settings, the case fatality rate rises to 1-3%, and in emergency or outbreak situations can reach 5-30%. 6
• Pneumonia and acute encephalitis are the leading causes of measles-related death. 1, 6
• Before widespread vaccination in the United States, measles caused approximately 500 deaths annually out of 500,000 reported cases. 6

High-Risk Populations

• Infants, young children under 3 years, and adults ≥20 years face the highest mortality risk. 1, 6
• Immunocompromised individuals (those with leukemia, lymphoma, HIV infection, or on immunosuppressive therapy) may develop severe, prolonged infection, sometimes without the typical rash. 1
• Pregnant women experience increased rates of premature labor, spontaneous abortion, low birth weight infants, and both maternal and fetal mortality. 1, 6
• Malnourished children, particularly in developing countries, have significantly elevated mortality risk. 6, 2

Diagnosis

• Laboratory confirmation relies on measles-specific IgM antibody testing in serum, dried blood spots, or oral fluid. 3, 5
• If initial IgM testing is negative within 72 hours of rash onset, repeat testing ≥72 hours after rash onset is required because early IgM may be undetectable. 1
• Detection of measles virus RNA by reverse transcriptase-polymerase chain reaction in throat swabs, nasopharyngeal swabs, urine, or oral fluid provides confirmatory diagnosis. 3, 5
• Viral isolation in culture or a four-fold increase in measles-specific IgG between acute and convalescent sera also confirms diagnosis. 5

Prevention

• Vaccination with measles-containing vaccine (MMR) is the cornerstone of measles prevention, with the first dose recommended at 12-15 months and the second dose at 4-6 years of age. 4, 1
• Post-exposure prophylaxis with MMR vaccine within 72 hours of exposure may provide protection or attenuate disease severity. 4, 1
• For susceptible contacts who cannot receive vaccine (pregnant women, severely immunocompromised individuals), intramuscular immune globulin at 0.25 mL/kg (maximum 15 mL) within 6 days of exposure is recommended; immunocompromised contacts require 0.5 mL/kg. 7, 1

Treatment

• There is no specific antiviral therapy for measles; management is primarily supportive care. 7, 3
• All children with clinical measles must receive vitamin A supplementation: 200,000 IU orally for children ≥12 months and 100,000 IU for children <12 months on day 1. 7, 1
• For complicated measles (pneumonia, otitis media, croup, severe diarrhea, or neurological problems), administer an identical second dose of vitamin A on day 2. 7
• Secondary bacterial infections require aggressive antibiotic treatment, oral rehydration therapy for diarrhea, and antipyretics (acetaminophen or ibuprofen, never aspirin in children) for fever control. 7, 1

Infection Control

• Immediate airborne isolation in a negative-pressure room with N95 respirators mandatory for all healthcare personnel is required, regardless of immunity status. 7, 1
• Healthcare workers without documented immunity must be excluded from work days 5-21 following exposure. 7, 1
• All suspected measles cases must be reported immediately to public health authorities, as a single case constitutes an urgent public health event. 1