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 Current Case Definition for
Surveillance
The current clinical case definition for measles
is: "An illness characterized by all of the
following clinical features: (a) a generalized rash
lasting three or more days, (b) a temperature of
38.3 C (101 F) or greater, (c) cough, or coryza,
or conjunctivitis." The laboratory criterion
for diagnosis is "isolation of measles virus
from a clinical specimen, or a significant rise
in measles antibody level by any standard serologic
assay, or positive serologic test for measles IgM
antibody." A confirmed case is "a case
that is laboratory confirmed or that meets the clinical
case definition and is epidemiologically linked
to a probable or confirmed case." Only confirmed
cases are reported, though suspect and probable
cases are investigated.
Photo Courtesy
of the Centers for Disease Control
Immunization
The first live and killed vaccines were licensed
in 1963. From 1968, only live vaccines have been
used in the United States. Most studies indicate
a clinical efficacy of 95% or greater in children
vaccinated with one dose at 15 months of age or
older. Vaccine efficacy may be slightly lower in
children immunized at 12 to 14 months of age, and
in those immunized with one dose given prior to
1980. Antibody has persisted for at least 17 years
in almost all persons immunized, and lifelong immunity
is expected. A two-dose immunization schedule for
measles has been recommended in the United States
since 1989.
 Maryland law requires immunization for
children in daycare programs, preschool programs
and in kindergarten through the twelfth grade. A
second dose is required for entry into grade kindergarten
through twelve.Based on the 1998/99 retrospective
kindergarten survey, an estimated 90% of children
in Maryland had received one dose of MMR by 24 months
of age (compared to 78% in the 1988/89 survey),
and 99% had received at least one dose by age 60
months.In 1998/99, schools in Maryland reported
that 99% of entrants into both kindergarten and
grade six had received a second dose of MMR.
Photo Courtesy of
the Centers for Disease Control
Historical Trends (see
graphs below)
In the pre-vaccine era in the United States, an
estimated three to four million cases of measles
occurred annually, and approximately 500,000 cases
and 500 deaths were reported annually, with epidemic
cycles every two to three years. Approximately 30%
of reported cases have one or more complications.
The most common causes of death are pneumonia in
children and encephalitis in adults. In recent years,
pneumonia has occurred in 1% to 5% of reported cases,
convulsions in 0.6% to 0.7%, and acute encephalitis
in one case per 1,000 reported measles cases.
In Maryland, there was extreme year-to-year fluctuation
in the number of reported measles cases during the
pre-vaccine era from 1907. There was also a steady
decline in the five-year mean incidence of measles
in Maryland from the late 1930's through the early
1970's. This decline in reported incidence over
several decades prior to vaccine licensure suggests
a similar downward trend in the completeness of
measles reporting in the state.
Epidemiology, 1988 - 1999 (see graphs
below)
There was a measles epidemic in Maryland from 1989
through 1991 which coincided with a nation-wide
epidemic. A total of 503 cases were reported in
the state during these three years. Measles incidence
has remained low after the epidemic, with 1-4 cases
per year since 1993. During the ten year period
(1988-1997), 36% of all reported cases were in pre-school
age children under age five, 30% in school age children,
and 34% in adults 18 years of age and above. Incidence
appears to have been age associated, with by far
the highest incidence in pre-schoolers, especially
in those less than 16 months of age (with 18% of
all cases). Among the 93 16 to 59 month-old cases
with known immunization status, only 13% had been
immunized prior to disease onset, while among the
116 school age cases with known immunization status,
90% had received at least one measles containing
immunization. Prior immunization status was unknown
among 45% of the 186 adult cases. A disease transmission
setting was reported for 57% of the 552 cases. Among
these 316 cases, transmission was reported to have
occurred in school in 36% of the cases, at home
in 26%, and in health care facilities (doctors'
offices, hospitals, and hospital emergency rooms)
in 22%.
The total number of measles cases reported to CDC
in 1998- 100 -was the lowest number ever recorded
in the United States. This reduction
in reported cases is part of an ongoing trend which,
according to CDC, "… may reflect cyclical
changes in measles incidence as well as increases
in measles vaccination coverage among school-aged
children, increased use of a second dose of measles
vaccine among school- and college-aged persons,
and increased efforts to control measles throughout
the Western Hemisphere." There were no cases
of measles reported in Maryland in 1999, and only
one was reported in 1998. This case was an international
importation. There has been no indigenous cases
of measles in Maryland for the past four years.
Figure
1. Reported Cases of Measles in Maryland, 1918-1999.
Figure
2. Measles Incidence, Maryland and United States.
Confirmed Cases, 1988-1999.
Figure
3. Measles Cases by Age and Immunization Status.
Confirmed Cases, 1988-1997. (n=552)
Figure
4. Measles Cases by Disease Transmission Setting.
Confimed Cases in Maryland, 1988-1997 Onset (n-552)
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