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Summary of Notifiable Diseases
United States 2002
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. 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. Disease reporting is likely
incomplete, and its completeness may vary depending on the disease. The
degree of completeness of data reporting may be 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 methods 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. Different racial/ethnic population groups may have differential
patterns of access to health care, potentially resulting in data that
are not representative of true racial/ethnic group-specific disease
incidence. 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, some disease programs collect race and
ethnicity as one variable; other programs collect these data as two variables.
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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