1 table, 1 figure omitted
Measles has not been endemic in the United States since 1997, although
limited outbreaks continue to be caused by imported* cases.1,2 In
2003, CDC assisted in investigating the largest school outbreak of measles
in the United States since 1998.3 The outbreak
consisted of 11 laboratory-confirmed cases: nine cases in a boarding school
in eastern Pennsylvania and two epidemiologically linked cases in New York
City (NYC). This report summarizes the results of the outbreak investigation,
which indicated that measles continues to be imported into the United States
and that high coverage with 2 doses of measles-containing vaccine (MCV) among
students was effective in limiting the size of the outbreak. Health-care providers
should maintain a high index of suspicion for measles, especially in those
who have traveled abroad recently, and recommendations for 2 doses of MCV
in all school-aged children should be followed.
In April 2003, the Pennsylvania Department of Health reported to CDC
two cases of measles in unvaccinated twins aged 13 years in a boarding school
with 663 students. Active surveillance for measles† was conducted in
the school, hospitals, and doctors' offices through May 2003. Patients were
interviewed, acute- and convalescent-phase sera were collected for measles
IgM enzyme-linked immunosorbent assay testing, and throat swabs and urine
samples were collected for viral genotyping. Efforts to control the outbreak
included vaccinating or excluding from campus and isolating all students and
staff members with no evidence of immunity to measles.‡ School and
personal vaccination records were reviewed to identify susceptible students
and staff members, respectively.
For evaluation of vaccine effectiveness, only students enrolled in the
school at the beginning of the outbreak were included. All staff members and
those students who received measles vaccination during the outbreak were excluded.
Vaccine effectiveness (VE) was calculated as VE (%) = [(ARU - ARV/ARU] ×
100, where ARU is the attack rate in unvaccinated persons and ARV is the attack
rate in students who had received 2 doses of MCV previously.4
A total of 11 laboratory-confirmed cases of measles were identified.
The source patient was a student aged 17 years who had received 2 doses of
MCV. On March 15, 2003, the student had returned to the United States from
Beirut, Lebanon, where measles was known to be circulating. He had cough and
fever the following day and rash on March 21, when he visited an emergency
department and was diagnosed with a viral exanthem. Upon returning to school,
the patient stayed at the school health center before returning to his dormitory.
Five persons with laboratory-confirmed measles were linked epidemiologically
to the source patient. These five included the unvaccinated twins who lived
in the same dormitory, the dormitory houseparent, and two other students in
different dormitories. One of these latter students infected two additional
students in his dormitory and an unvaccinated child aged 13 months in NYC,
who was linked epidemiologically to an unvaccinated immigrant aged 33 years,
who was diagnosed with measles and who lived in the same apartment building.
The ninth school patient was linked epidemiologically to, and might have been
infected by, any one of five infected persons from different dormitories.
All nine measles cases in the school were confirmed serologically. Measles
genotype D4 was identified in two school patients and the child in NYC. The
last date of rash onset in a boarding school patient was April 15 (Figure).
No deaths or major complications were reported; two students with measles,
who were unvaccinated because of religious exemptions, required hospitalization
The median age of the nine patients in the school was 17 years (range:
13-26 years). Of the nine, two had not received any doses of MCV, one had
received 1 dose, and six had received 2 doses. Patients with 1 or 2 doses
of MCV had milder illness than unvaccinated patients, including a shorter
duration of rash (median: 5 days versus 10 days; p<0.05) and fewer days
of school or work missed (median: 5 days versus 8 days; p<0.05) (Table).
Of the 663 students in the boarding school, eight (1.2%) students had
never received any doses of MCV, 26 (3.9%) students had received 1 dose, and
629 (94.9%) students had received 2 doses before the outbreak. Thus, vaccine
coverage for 2 doses was 94.9% and for ≥1 dose was 98.8%. Vaccination with
measles, mumps, and rubella vaccine was begun on April 3. Of the eight unvaccinated
students, four had claimed religious or philosophical exemptions. Of these
four students, two contracted measles, one was excluded from the school, and
one was vaccinated during the outbreak. All of the remaining four unvaccinated
students who did not claim any exemptions were vaccinated during the outbreak
as well as other susceptible students and staff members.
Excluding five previously unvaccinated students who were vaccinated
during the outbreak and two students who had 2 doses of MCV previously but
were inadvertently revaccinated during the outbreak, the measles attack rate
was 66.7% (two of three) among unvaccinated students and 1.0% (six of 627)
among students who had received 2 doses of MCV. All vaccinees with 1 dose
of MCV received a second dose during the outbreak; no measles cases were diagnosed
among these students. VE was 98.6% among students who had received 2 doses
P Lurie, MD, P Britz, J Bowen, P Tran, MEd, H Stafford, Pennsylvania
Dept of Health. YA Gillan, DrPH, New York City Dept of Health and Mental Hygiene.
W Bellini, PhD, P Rota, PhD, J Rota, MPH, Div of Viral and Rickettsial Diseases,
National Center for Infectious Diseases; E Eduardo, MPH, National Center for
HIV, STD, and TB Prevention; G Dayan, MD, S Redd, M Papania, MD, J Seward,
MBBS, Epidemiology and Surveillance Div, National Immunization Program; RJ
Berry, MD, Birth Defects and Developmental Disabilities Div, National Center
on Birth Defects and Developmental Disabilities; L Yeung, MD, EIS Officer,
Measles is rare in the United States, with only 42 confirmed cases in
2003, according to provisional data.2 The
limited outbreak described in this report highlights both the success of the
U.S. vaccination program and the continuing risk for imported measles despite
a high immunity among the U.S. population. The last reported U.S. school outbreak
occurred in 2000 and involved nine persons, including six high school students.1 Five of those six student patients had received
only 1 dose of MCV, which was in compliance with state requirements at that
Before 1989, when the Advisory Committee on Immunization Practices recommended
a routine 2-dose MCV schedule for school-aged children, larger measles outbreaks
with >100 cases occurred in schools.5,6 All
states but one now require 2 doses of MCV for children attending school.7 However, exemptions for religious or philosophical
reasons are permitted in the majority of states, resulting in exemption for
0.6% of the nation's children.8 These children
have a higher likelihood of acquiring and spreading measles than those who
have been vaccinated.9
In the outbreak described in this report, consistent with previous evaluations,10 2 doses of MCV were highly effective in preventing
the spread of measles, although a substantial number of exposed students,
combined with a 1% failure rate among recipients with 2 doses, resulted in
two generations of transmission in the school. Recipients of 2 doses of MCV
had milder symptoms and shorter duration of illness than unvaccinated patients.
Two unvaccinated students were hospitalized for dehydration, but none of the
vaccinated students required hospitalization.
If an outbreak occurs, all persons whose illness is consistent with
the definition for suspected§ measles should be tested for both measles
IgM and measles virus by culture or reverse transcriptase polymerase chain
reaction. A convalescent serum should be obtained if the acute IgM is negative.
This investigation highlighted the importance of viral specimens to document
importation from overseas, confirm spread of the same genotype to NYC, and
provide continued evidence for the absence of endemic transmission in the
This outbreak of measles was caused by importation; the source patient
was infected in Lebanon. Although the patient had classic signs for the disease
(e.g., fever, rash, cough, and coryza), measles was not diagnosed initially,
and the outbreak was not recognized until two unvaccinated students were hospitalized.
A history of recent travel outside the United States should raise suspicion
for a diagnosis of measles in a patient with appropriate clinical signs, regardless
of vaccination status.
*An imported case of measles has its source outside the country, rash
onset occurs within 21 days of entering the country, and illness cannot be
linked to local transmission.
†Surveillance was conducted by using the 1997 case definition
for measles issued by CDC and the Council of State and Territorial Epidemiologists:
illness characterized by a generalized maculopapular rash lasting ≥3 days;
a temperature of ≥101.0°F (≥38.3°C); and cough, coryza, or conjunctivitis.
‡Students and staff members were classified as having no evidence
of measles immunity if they were born after 1957 and could not document history
of physician-diagnosed measles illness, positive serology of measles IgG,
history of 2 doses of MCV at least 28 days apart (students), or 1 dose (adults)
with the first dose at or after age 1 year.
§Suspected measles is a febrile illness with a generalized maculopapular
Measles Outbreak in a Boarding School—Pennsylvania, 2003. JAMA. 2004;291(22):2694-2696. doi:10.1001/jama.291.22.2694