Update: Measles --- United States, January--July 2008
Sporadic importations of measles into the United States have occurred since the disease was declared eliminated from
the United States in 2000 (
1). During January--July 2008, 131 measles cases were reported to CDC, compared with an average
of 63 cases per year during 2000--2007.* This report
updates an earlier report on measles in the United States during 2008
2) and summarizes two recent U.S outbreaks among unvaccinated school-aged children. Among those measles cases
reported during the first 7 months of 2008, 76% were in persons aged <20 years, and 91% were in persons who were
unvaccinated or of unknown vaccination status. Of the 131 cases, 89% were imported from or associated with importations from
other countries, particularly countries in Europe, where several outbreaks are ongoing
3,4). The findings demonstrate that
measles outbreaks can occur in communities with a high number of unvaccinated persons and that maintaining high overall
measles, mumps, and rubella (MMR) vaccination coverage rates in the United States is needed to continue to limit the spread
Measles cases in the United States are reported by state health departments to CDC using standard case
definitions† and case classifications. Cases acquired outside the United States are categorized as importations. Those acquired inside the
United States are considered importation associated if they are linked epidemiologically via a chain of transmission to an
importation or have virologic evidence of
importation.§ Other cases are classified as having an unknown source. In the United
States, recommendations for MMR vaccination include a single dose at age 12--15 months and a second dose at the time of
school entry (
5). Vaccination as early as age 6 months is recommended for U.S. children traveling abroad and is
sometimes recommended within U.S. communities during outbreaks of measles.
During January 1--July 31, 2008, 131 measles cases were reported to CDC from 15 states and the District of
Columbia (DC): Illinois (32 cases), New York (27), Washington (19), Arizona (14), California (14), Wisconsin (seven), Hawaii
(five), Michigan (four), Arkansas (two), and DC, Georgia, Louisiana, Missouri, New Mexico, Pennsylvania, and Virginia (one
each). Seven measles outbreaks (i.e., three or more cases linked in time or place) accounted for 106 (81%) of the cases.
Fifteen of the patients (11%) were hospitalized, including four children aged <15 months. No deaths were reported.
Among the 131 cases, 17 (13%) were importations: three each from Italy and Switzerland; two each from Belgium,
India, and Israel; and one each from China, Germany, Pakistan, the Philippines, and Russia. This is the lowest percentage
of imported measles cases since 1996 (Figure 1). Nine of the importations were in U.S. residents who had traveled abroad,
and eight were in foreign visitors. An additional 99 (76%) of the 131 cases were linked epidemiologically to importations or
had virologic evidence of importation. The source of measles acquisition of 15 cases (11%) could not be determined.
Among the 131 measles patients, 123 were U.S. residents, of whom 99 (80%) were aged <20 years
Five (4%) of the 123 patients had received 1 dose of MMR vaccine, six
(5%) had received 2 doses of MMR vaccine, and 112 (91%) were
unvaccinated or had unknown vaccination status. Among these 112
patients, 95 (85%) were eligible for vaccination, and 63 (66%) of those
were unvaccinated because of philosophical or religious beliefs (Figure 2).
Washington. On April 28, 2008, the Washington State
Department of Health received a report of several suspected measles
cases in a Grant County household. The index patient had rash onset on
April 12. During April 18--21, the other seven children in the
household became ill with fever and rash. Three of the children
developed pneumonia and were evaluated by a health-care provider who
suspected measles; all three tested positive for measles-specific IgM
antibody. Rash onset occurred during April 13--May 30 in 11 additional
cases identified in Grant County. All of the 19 cases were linked
epidemiologically, and all but one occurred in children and adolescents
aged 9 months to 18 years. The 19 cases included 16 in school-aged
children, among whom 11 were home schooled. Because of their parents'
philosophical or religious beliefs, none of the 16 children had
received measles-containing vaccine. Specimens from eight patients were
submitted for virologic testing, and all contained genotype D5, which
had been circulating in Japan and parts of Europe. A possible source of
the outbreak was a church conference, held March 25--29 in King County,
Washington, that was attended by four of the patients, including the
index patient. The conference was attended by approximately 3,000
persons, primarily students from junior high through university age
from 18 states, DC, and several foreign countries. None of these
countries or states has since reported confirmed cases of measles among
persons who attended this conference.
Illinois. On May 19, 2008, the Illinois Department of
Public Health was notified by the DuPage County Health Department about
a suspected case of measles. By May 27, four confirmed cases of measles
had been reported to the county, three of which were laboratory
confirmed. Among the four cases, rash onsets occurred during May
17--19, suggesting a common exposure. The four patients were
unvaccinated girls aged 10--14 years; all had attended an event May 5
and might have attended a home gathering 2 days earlier. Both events
were attended by a teenager who had recently returned from Italy and
reportedly had developed fever and rash. Although attempts to obtain
further information about the traveler were unsuccessful, viral
isolation from one of the four patients yielded genotype D4, a strain
circulating in Italy. Through July 31, 26 additional measles cases were
reported, all with epidemiologic links to the first four cases. Among
the 30 cases, 14 were confirmed in DuPage County, 11 in suburban Cook
County, and five in Lake County. One case occurred in a person aged 43
years. The remaining 29 cases were in persons aged 8 months--17 years,
including 25 (83%) school-aged children, all of whom were home schooled
and not subject to school-entry vaccination requirements. Because of
their parents' beliefs against vaccination, none of the 25 had received
MA Grigg, AL Brzezny, MD, Grant County
Health District; J Dawson, PhD, Chelan-Douglas Health District; K
Rietberg, MPH, Public Health -- Seattle & King County; C DeBolt,
MPH, Washington State Dept of Health. P Linchangco, MPH, S Smith, MPH,
S Jones, M Vernon, DrPH, C Counard, MD, Cook County Dept of Public
Health; R Chugh, MD, S Nelson, MPH, K Green, C Petit, J Vercillo,
DuPage County Health Dept; S Cesario, Lake County Health Dept; K Hunt,
C Conover, MD, J Daniels, K McMahon, Illinois Dept of Public Health. SB
Redd, KM Gallagher, DSc, GL Armstrong, MD, LJ Anderson, MD, JF Seward,
MBBS, PA Rota, PhD, JS Rota, MPH, L Lowe, MS, WJ Bellini, PhD, Div of
Viral Diseases, National Center for Immunization and Respiratory
The number of measles cases reported during January 1--July
31, 2008, is the highest year-to-date since 1996. This increase was not
the result of a greater number of imported cases, but was the result of
greater viral transmission after importation into the United States,
leading to a greater number of importation-associated cases. These
importation-associated cases have occurred largely among school-aged
children who were eligible for vaccination but whose parents chose not
to have them vaccinated. One study has suggested an increasing number
of vaccine exemptions among children who attend school in states that
allow philosophical exemptions (
6). In addition, home-schooled children are not covered by
school-entry vaccination requirements in many states. The increase in
importation-associated cases this year is a concern and might herald a
larger increase in measles morbidity, especially in communities with
many unvaccinated residents.
In the United States, measles caused 450 reported deaths and 4,000 cases of encephalitis annually before measles
vaccine became available in the mid-1960s
1). Through a successful measles vaccination program, the United States
eliminated endemic measles transmission (
1). Sustaining elimination requires maintaining high MMR vaccine coverage rates,
particularly among preschool (>90% 1-dose coverage) and school-aged children (>95% 2-dose coverage)
High coverage levels provide herd immunity, decreasing everyone's risk
for measles exposure and affording protection to persons who cannot be
vaccinated. However, herd immunity does not provide 100% protection,
especially in communities with large numbers of unvaccinated persons.
For the foreseeable future, measles importations into the United States
will continue to occur because measles is still common in Europe and
other regions of the world. Within the United States, the current
national MMR vaccine coverage rate is adequate to prevent the sustained
spread of measles. However, importations of measles likely will
continue to cause outbreaks in communities that have sizeable clusters
of unvaccinated persons.
Measles is one of the first diseases to reappear when vaccination coverage rates fall. Ongoing outbreaks are occurring
in European countries where rates of vaccination coverage are lower than those in the United States, including Austria, Italy,
and Switzerland (
3,4). In June 2008, the United Kingdom's Health Protection Agency declared that, because of a drop
in vaccination coverage levels (to 80%--85% among children aged 2 years), measles was again endemic in the United
3,8), 14 years after it had been eliminated. Since April 2008, two measles-related deaths have been reported in Europe,
both in children ineligible to receive MMR vaccine because of congenital immunologic compromise
children depend on herd immunity for protection from the disease, as do
children aged <12 months, who normally are too young to receive the
vaccine. Otherwise healthy children with measles also are at risk for
severe complications, including encephalitis and pneumonia, which can
lead to permanent disability or death.
The measles outbreaks in Illinois and Washington demonstrate that measles remains a risk for unvaccinated persons
and those who come in contact with them
9,10). Each school year, parents should ensure that their children's vaccinations
are current, regardless of whether the children are returning to school, attending day care, or being schooled at home.
Adults without evidence of measles
should receive at least 1 dose of MMR vaccine. All persons who travel
internationally also should be up-to-date on their measles vaccination
and other vaccinations recommended for countries they might visit.
These recommendations include a single dose of MMR vaccine for infant
travelers aged 6--11 months and 2 doses, administered at least 28 days
apart, for children aged
>12 months (
- Orenstein WA, Papania MJ, Wharton ME. Measles elimination in the United States. J Infect Dis 2004;189(Suppl1):S1--3.
- CDC. Measles---United States, January 1--April 25, 2008. MMWR 2008;57:494--8.
- EuroSurveillance Editorial Team. Measles once again endemic in the United Kingdom. Eurosurveillance 2008;13:1. Available at
- Filia A, De Crescenzo M, Seyler T, et al. Measles resurges in Italy: preliminary data from September 2007 to May 2008.
Eurosurveillance 2008;13:pii=18928. Available at
Measles, mumps, and rubella---vaccine use and strategies for
elimination of measles, rubella, and congenital rubella syndrome and
control of mumps: recommendations of the Advisory Committee on
Immunization Practices (ACIP). MMWR 1998;47(No. RR-8).
- Omer SB, Pan WKY, Halsey NA, et al. Nonmedical exemptions to
school immunization requirements: secular trends and association of
state policies with pertussis incidence. JAMA 2006;296:1757--63.
- Gay NJ. The theory of measles elimination: implications for the
design of elimination strategies. J Infect Dis 2004;189(Suppl1)S27--35.
- UK Health Protection Agency. Confirmed measles cases in England
and Wales---an update to end-May 2008. Health Protection Report
2008;2(25). Available at http://www.hpa.org.uk/hpr/archives/2008/news2508.htm.
- Parker AA, Staggs W, Dayan GH, et al. Implications of a 2005
measles outbreak in Indiana for sustained elimination of measles in the
United States. N Engl J Med 2006;355:447--55.
- Dayan GH, Ortega-Sanchez IR, LeBaron CW, Quinlisk MP, Iowa Measles
Response Team. The cost of containing one case of measles: the economic
impact on the public health infrastructure---Iowa, 2004. Pediatrics
* Based on nationally notifiable disease data for 2000--2007.
† CDC/Council of State and Territorial
Epidemiologists measles clinical case definition: an illness
characterized by a generalized maculopapular rash for
>3 days, a temperature of
>38.3°C), and cough, coryza, or conjunctivitis. A case is considered confirmed if it is laboratory confirmed (using serologic or
virologic methods) or if it meets the clinical case definition and is epidemiologically linked to a confirmed case.
§ A case is considered to have virologic evidence of
importation if it is within a chain of transmission from which a
measles virus is identified that is not endemic in the United States.
¶ Documented receipt of 2 doses of live measles
virus vaccine, laboratory evidence of immunity, documentation of
physician-diagnosed measles, or birth before 1957.
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Date last reviewed: 8/20/2008