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Summary of Notifiable Diseases
United States 2001
Interpreting Data
Incidence data in the Summary are presented by
the date of report to CDC as determined by the MMWR week and year assigned
by the state or territorial health department. As a result, annual incidence
data in the Summary represent cases with onset during the MMWR
year assigned to the case, or during previous years. In addition, data
in the Summary are reported by the state in which the patient
resides at the time of diagnosis. For many of the nationally notifiable
infectious diseases, surveillance data are independently reported to EPO
and other CDC programs. Thus, surveillance data reported by other CDC programs
may vary from data reported in the Summary because of differences
in 1) the date used to aggregate data (e.g., date of report, date of disease
occurrence), 2) the timing of reports, 3) the source of the data, 4) surveillance
case definitions, and 5) policies regarding case jurisdiction (i.e., which
state should report the case to CDC).
The data reported in the Summary are useful for analyzing disease trends
and determining relative disease burdens. However, these data must be interpreted
in light of reporting practices. Some diseases that cause severe clinical illness
(e.g., plague and rabies) are most likely reported accurately if they were diagnosed
by a clinician. However, persons who have diseases that are clinically mild and
infrequently associated with serious consequences (e.g., salmonellosis) might
not seek medical care from
a health-care provider. Even if these less severe diseases are diagnosed, they
are less likely to be reported.
The degree of completeness of data reporting also is influenced by the diagnostic
facilities available; the control measures in effect; public awareness of a specific
disease; and interests, resources, and priorities of state and local officials
responsible for disease control and public health surveillance. Finally, factors
such as changes in the case definitions for public health surveillance, introduction
of new diagnostic tests, or discovery of new disease entities can cause changes
in disease reporting that are independent of the true incidence of disease.
Public health surveillance data are published for selected racial and ethnic
population groups because these variables can be risk markers for certain notifiable
diseases. Race and ethnicity data can also be used to highlight populations for
focused prevention efforts. However, caution must be used when drawing conclusions
from reported race and ethnicity data. Certain racial/ethnic population groups
have differential patterns of access to health care, potentially resulting in
data that are not representative of disease incidence in these populations. Surveillance
data reported to NNDSS are either in individual case-specific form or summary
form (aggregated data for a group of cases). Summary data often lack demographic
information (e.g., race); therefore, the demographic-specific incidence rates
presented in the Summary may be underestimated.
In addition, not all race and ethnicity data are collected uniformly
for all
diseases. For example, in NCHSTP, the Division of HIV/AIDS Prevention —Surveillance
and Epidemiology and the Division of Sexually Transmitted Diseases Prevention
collect race/ethnicity data using a single variable. A person's race/ethnicity
is reported as American Indian/Alaska Native, Asian/Pacific Islander, black non-Hispanic,
white non- Hispanic, or Hispanic. Additionally, although the recommended standard
for classifying a person's race or ethnicity is based on self-reporting, this
procedure might not always be followed.
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