Measles

Measles, also known as rubeola, is one of the most contagious infectious diseases, with at least a 90% secondary infection rate in susceptible domestic contacts. It can affect people of all ages, despite being considered primarily a childhood illness. Measles is marked by prodromal fever, cough, coryza, conjunctivitis, and pathognomonic enanthem (ie, Koplik spots), followed by an erythematous maculopapular rash on the third to seventh day. Infection confers life-long immunity.


A generalized immunosuppression that follows acute measles frequently predisposes patients to bacterial otitis media and bronchopneumonia. In approximately 0.1% of cases, measles causes acute encephalitis. Subacute sclerosing panencephalitis (SSPE) is a rare chronic degenerative disease that occurs several years after measles infection.

After an effective measles vaccine was introduced in 1963, the incidence of measles decreased significantly. Nevertheless, measles remains a common disease in certain regions and continues to account for nearly 50% of the 1.6 million deaths caused each year by vaccine-preventable childhood diseases. The incidence of measles in the United States and worldwide is increasing, with outbreaks being reported particularly in populations with low vaccination rates.
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Maternal antibodies play a significant role in protection against infection in infants younger than 1 year and may interfere with live-attenuated measles vaccination. A single dose of measles vaccine administered to a child older than 12 months induces protective immunity in 95% of recipients. Because measles virus is highly contagious, a 5% susceptible population is sufficient to sustain periodic outbreaks in otherwise highly vaccinated populations.


A second dose of vaccine, now recommended for all school-aged children in the United States,[2] induces immunity in about 95% of the 5% who do not respond to the first dose. Slight genotypic variation in recently circulating strains has not affected the protective efficacy of live-attenuated measles vaccines.

Unsubstantiated claims that suggest an association between the measles vaccine and autism have resulted in reduced vaccine use and contributed to a recent resurgence of measles in countries where immunization rates have fallen to below the level needed to maintain herd immunity.


Considering that for industrialized countries such as the United States, endemic transmission of measles may be reestablished if measles immunity falls to less than 93-95%, efforts to ensure high immunization rates among people in both developed and developing countries must be sustained.


Supportive care is normally all that is required for patients with measles. Vitamin A supplementation during acute measles significantly reduces risks of morbidity and mortality.


For patient education resources, see Bacterial and Viral Infections, as well as Measles and Skin Rashes in Children
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Etiology

The cause of measles is the measles virus, a single-stranded, negative-sense enveloped RNA virus of the genus Morbillivirus within the family Paramyxoviridae. Humans are the natural hosts of the virus; no animal reservoirs are known to exist. This highly contagious virus is spread by coughing and sneezing via close personal contact or direct contact with secretions.

Risk factors for measles virus infection include the following:

Children with immunodeficiency due to HIV or AIDS, leukemia, alkylating agents, or corticosteroid therapy, regardless of immunization status
Travel to areas where measles is endemic or contact with travelers to endemic areas
Infants who lose passive antibody before the age of routine immunization

Risk factors for severe measles and its complications include the following:

Malnutrition
Underlying immunodeficiency
Pregnancy
Vitamin A deficiency
Epidemiology
United States statistics


The practice of administering 2 doses of live-attenuated measles vaccine to children to prevent school outbreaks of measles was implemented when the vaccine was first licensed in 1963. The immunization program resulted in a decrease of more than 99% in reported incidence.


From 1989 to 1991, a major resurgence occurred, affecting primarily unvaccinated preschoolers. This measles resurgence resulted in 55,000 cases and 130 deaths[7] and prompted the recommendation that a second dose of measles vaccine be given to preschoolers in a mass vaccination campaign that led to the effective elimination in the United States of endemic transmission of the measles virus.[8]


By 1993, vaccination programs had interrupted the transmission of indigenous measles virus in the United States; since then, most reported cases of measles in the United States have been linked to international travel.[9] By 1997-1999, the incidence of measles had been reduced to a historic low (< 0.5 cases per million persons). From 1997 to 2004, the reported incidence was as low as 37-116 cases per year. From November 2002 on, measles was not considered an endemic disease in the United States.


From 2000 through 2007, an average of 63 cases were reported annually to the US Centers for Disease Control and Prevention (CDC). In 2004, 34 cases were reported; after that all-time low, however, the annual incidence began to increase, with most cases linked either directly or indirectly to international travel. Incomplete vaccination rates facilitate the spread once the virus is imported to the United States.


In 2005, 66 cases of measles were reported to the CDC.[10] Of these, 34 were linked with a single outbreak in Indiana associated with the return of an unvaccinated 17-year-old American traveling in Romania. In 2006, a total of 49 confirmed cases were reported in the United States.


From January to June 2008, 131 cases of measles were reported to the CDC.[11] Although 90% of those 131 cases were associated with importation of the virus to the United States from overseas, 91% of those affected were unvaccinated or had unknown or undocumented vaccination status. At least 47% of the 131 measles infections were in school-aged children whose parents chose not to have them vaccinated.[11]


In the period from January 1 to May 20, 2011, a total of 118 cases were reported to the CDC; this represents the highest reported number of measles cases for the same period since 1996.[12] Of the 118 cases, 105 (89%) were associated with importation; the source of the remaining 13 cases could not be ascertained. In all, 105 (89%) of the 118 patients were unvaccinated; 24 (20%) were persons 12 months to 19 years of age whose parents claimed a religious or personal exemption.


Approximately half of the 118 cases—58, or 49%—were accounted for by 9 outbreaks. The largest of these outbreaks involved 21 persons in Minnesota, in a setting where parental concerns about the safety of measles, mumps, and rubella (MMR) vaccine caused many children to go unvaccinated.[13] As a result of this outbreak, many persons were exposed, and at least 7 infants too young to receive MMR vaccine were infected.


Despite the highest recorded immunization rates in history, young children who are not appropriately vaccinated may experience more than a 60-fold increase in risk of disease due to exposure to imported measles cases from countries that have not yet eliminated the disease.
International statistics


In developing countries, measles affects 30 million children a year and causes 1 million deaths. Measles causes 15,000-60,000 cases of blindness per year.


In 1998, the cases of measles per 100,000 total population reported to the World Health Organization (WHO) was 1.6 in the Americas, 8.2 in Europe, 11.1 in the Eastern Mediterranean region, 4.2 in South East Asia, 5.0 in the Western Pacific region, and 61.7 in Africa. In 2006, only 187 confirmed cases were reported in the Western Hemisphere (mainly in Venezuela, Mexico, and the United States).[14]


Between 2000 and 2008, the number of worldwide measles cases reported to the WHO and the United Nations Children’s Fund (UNICEF) declined by 67% (from 852,937 to 278,358). During the same 8-year period, global measles mortality dropped by 78%. However, it is believed that global measles incidence and mortality remain underreported, with many countries, particularly those with the highest disease burden, lacking complete, reliable surveillance data.[15]


Since 2008, France has been experiencing an outbreak of measles, which has not yet begun to slacken.[16] Over the same period, outbreaks have also been occurring in the 46 countries of the WHO African Region.[17] Worldwide, most reported cases of measles continue to be from Africa.
Age-related demographics


Although measles is historically a disease of childhood, infection can occur in unvaccinated or partially vaccinated individuals of any age or in those with compromised immunity.


Unvaccinated young children are at the highest risk. Age-specific attack rates may be highest in susceptible infants younger than 12 months, school-aged children, or young adults, depending on local immunization practices and incidence of the disease. Complications such as otitis media, bronchopneumonia, laryngotracheobronchitis (ie, croup), and diarrhea are more common in young children.


Of the 66 cases of measles reported in the United States in 2005, 7 (10.6%) involved infants, 4 (6.1%) involved children aged 1-4 years, 33 (50%) involved persons aged 5-19 years, 7 (10.6%) involved adults aged 20-34 years, and 15 (22.7%) involved adults older than 35 years.[10]


Among the 118 US patients reported to have measles between January 1 and May 20, 2011, age ranged from 3 months to 68 years.[12] More than half were younger than 20 years: 18 (15%) were younger than 12 months, 24 (20%) were 1-4 years old, 23 (19%) were 5-19 years old, and 53 (45%) were 20 years of age or older.


In heavily populated, underdeveloped countries, measles is most common in children younger than 2 years.

Sex- and race-related demographics

Unvaccinated males and females are equally susceptible to infection by the measles virus. Excess mortality following acute measles has been observed among females at all ages, but it is most marked in adolescents and young adults. Excessive non–measles-related mortality has also been observed among female recipients of high-titer measles vaccines in Senegal, Guinea Bissau, and Haiti.[18]


Measles affects people of all races.

Prognosis

The prognosis for measles is generally good, with infection only occasionally being fatal. The CDC reports the childhood mortality rate from measles infection in the United States to be 0.1-0.2%. However, many complications and sequelae may develop (see Complications), and measles is a major cause of childhood blindness in developing countries.


Globally, measles remains one of the leading causes of death in young children. According to the CDC, measles caused an estimated 197,000 deaths worldwide in 2007.[14] An estimated 85% of these deaths occurred in Africa and Southeast Asia. From 2000-2007, deaths worldwide fell by 74% (to 197,000 from an estimated 750,000), thanks to the partnership of several global organizations.


Case-fatality rates are higher among children younger than 5 years. The highest fatality rates are among infants aged 4-12 months and in children who are immunocompromised because of human immunodeficiency virus (HIV) infection or other causes.


Complications of measles are more likely to occur in persons younger than 5 years or older than 20 years, and morbidity and mortality are increased in persons with immune deficiency disorders, malnutrition, vitamin A deficiency, and inadequate vaccination.


Croup, encephalitis, and pneumonia are the most common causes of death associated with measles. Measles encephalitis, a rare but serious complication, has a 10% mortality.