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Measles
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 criteria 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.
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.
Immunization is required by Maryland law for children
in preschool programs and in kindergarten through the
twelfth grade, and a requirement for a second dose for
entry into all grades is currently being phased in.
Based on the 1993/94 retrospective kindergarten survey,
an estimated 86% 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 1993/94, schools in Maryland
reported that 99% of entrants into both kindergarten
and grade six had received a second dose of MMR.
Historical Trends (see graphs)
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. 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 - 1993
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. During the six year period, approximately
one third of all reported cases were in pre-school age
children under age five, one third in school age children,
and one third 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
under 16 months of age (with 18% of all cases). Among
the 90 16 to 59 month old cases with known immunization
status, only 12% had been immunized prior to disease
onset, while among the 115 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 183 adult cases. The mean annual
incidence during this six year period was over three
times as high in Cecil County, with 69 cases, as in
Garrett County, the county with the next highest incidence.
A disease transmission setting was reported for 58%
of the 543 cases. Among these 314 cases, transmission
was reported to have occurred in school in 36% of the
cases, at home in 25%, and in health care facilities
(doctors' offices, hospitals, and hospital emergency
rooms) in 22%.
The CDC reports that "the total number of measles
cases reported to CDC in 1993-312-was the lowest number
ever recorded in the United States. This reduction in
reported measles cases 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."
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Mumps
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