Introduction & Methods
 Current Case Definitions
for Surveillance
Nine diseases for which children are currently routinely
immunized are reportable by law in Maryland. With the
exception of invasive Haemophilus influenzae type
b disease, surveillance for these illnesses in the state
is passive, depending on physicians, hospitals, and laboratories
to report cases to the local health departments (LHDs).
The LHDs then report cases to the Epidemiology and Disease
Control Program (EDCP), Maryland Department of Health
and Mental Hygiene (DHMH), which transmits data to the
Centers for Disease Control and Prevention (CDC). The
current case definitions for surveillance are quoted from
Case Definitions for Infectious Conditions Under Public
Health Surveillance, MMWR 1997, volume 46, number
RR-10.
Immunization
Maryland immunization requirements for school entry,
and vaccination coverage levels are discussed in the "Immunization
Levels" section of this report. Information on immunization
coverage is obtained from surveys of two-year olds and
annual retrospective school enterer surveys. There is
much less information available about the immunization
status of Maryland residents than there is regarding their
morbidity from vaccine preventable diseases. No data are
available regarding the current immunization status of
the state's adult population.
Included in each vaccine preventable disease morbidity
report is information on the vaccination status of the
patient, if available. Data is collected on CDC surveillance
forms and recorded electronically in Maryland’s communicable
disease surveillance system. In this report, Immunization
status of patients is presented for measles and pertussis.
Information on vaccines is obtained from the following
CDC publications: Recommendations of the Advisory Committee
on Immunization Practices (ACIP), Manual for the Surveillance
of Vaccine Preventable Diseases, Epidemiology and Prevention
of Vaccine Preventable Diseases.
Historical Trends
For each disease, graphs are included of the trends in
the number of cases and in rates, going as far back as
EDCP data allows. The growth of Maryland’s total
population, from an estimated 1.3 million in 1907 to 5.17
million in 1999, is controlled for in the data on rates,
though these do not reflect trends within high-risk groups
(such as infants and children).
Long-term trends in case numbers and rates reflect changes
in health care seeking behavior, diagnostic practice,
case definition, and surveillance system sensitivity and
specificity, as well as changes in incidence. For example,
steeply rising incidence in the early part of the century
during the first decade or so after the first year for
which morbidity data are available suggests rapidly increasing
surveillance program sensitivity during this period for
several diseases. It also appears likely that the dramatic
peak in reported pertussis cases in 1985 was more the
result of a pertussis study in Baltimore City and Baltimore
County involving active case detection with routine culturing,
and thus greatly increased surveillance program sensitivity,
than the result of a real increase in incidence.
The introduction of active surveillance for invasive
H. flu disease in November 1991 is also likely to have
increased the reporting rate for this condition. Unfortunately,
the inadequate documentation of changes in practices which
may have led to changing surveillance program sensitivity
makes it difficult to interpret trends in reported incidence.
Maryland's annual notifiable disease reporting forms
suggest that the annual totals were reported by year of
case report through 1968 and by year of case onset
from 1969 to 1993, then again by year of report
from 1994 through the present.
Data on the trends in mortality due to vaccine preventable
diseases are not included because the classification of
cause of death is even more sensitive to changes in practices
over time than is the case for morbidity, and because
trends in cause-specific mortality also reflect improvement
in treatment and reductions in case fatality rates over
time.
Epidemiology, 1988/89
– 1999
Graphs are included of the numbers of cases and rates
by year of disease onset or disease report (depending
on year, as discussed above), age group, and county of
residence for invasive H. flu disease, acute hepatitis
B, measles, mumps, and pertussis in Maryland from 1988
or 1989 to 1999. The Centers for Disease Control and Prevention
publish surveillance data for the United States on the
numbers of cases and "incidence" by year of
case report rather than by year of onset. Although comparative
trends in "incidence" in Maryland and the United
States as a whole during this period may reflect important
trends in actual incidence, differences in incidence between
the state and the U.S. may reflect differing surveillance
system sensitivities as well.
Data on measles through 1994 were abstracted from the
EDCP Immunization Division's "Rash File" database,
and data on the immunization status of pertussis cases
through 1994 from the Division's pertussis database. H.
flu serotype-specific data were abstracted from the database
of the Bacterial Invasive Diseases Surveillance Project
of The Johns Hopkins University, School of Hygiene and
Public Health, and the EDCP. All other data were abstracted
from the Maryland Electronic Reporting and Surveillance
System (MERSS) database maintained by the EDCP Division
of Communicable Disease Surveillance.
The numbers of cases of disease by year presented here
often differ somewhat from the numbers officially reported
annually by the EDCP. The main reason for these differences
is the deletion in the numbers documented here of second
reports of cases reported during two consecutive years.
More information on the vaccine preventable diseases
reported each year in Maryland is published in the monthly
issues of the Maryland Medical Journal, generally beginning
with the May/June or July issues.
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