ses Surveillance System (NNDSS) each week (Table 1).
We describe disease-specific trends in demographic characteristics and geographic and seasonal distribution of selected conditions caused by critical biologic agents reported to NNDSS. These diseases and conditions include anthrax, botulism, brucellosis, cholera, plague, tularemia, and selected viral encephalitides. By identifying patterns of endemic disease associated with critical agents, we establish a baseline against which future disease incidence can be compared. This process should allow easier identification of unusual reports of disease incidence, which in turn will enhance the ability of the public health community to identify and investigate outbreaks.
Data and Sources
We analyzed NNDSS data voluntarily reported to CDC from state health departments from 1992 to 1999 (11). As of 1999, a total of 56 infectious diseases or conditions with public health surveillance case definitions (12,13) were considered nationally notifiable, as agreed upon by the Council of State and Territorial Epidemiologists and CDC (14). Each year, the Council and CDC review the list of nationally notifiable infectious diseases to determine whether conditions should be added or removed as new pathogens emerge or disease incidence changes (15). Based on state-specific health priorities, each state independently determines which of the nationally notifiable diseases should be made notifiable (i.e., legally reportable by healthcare providers or laboratories to the public health system within their jurisdiction). As a result, not all nationally notifiable diseases are legally reportable in all states. With some variation by jurisdiction, the completeness of public health surveillance is dependent on healthcare providers and laboratories submitting disease incidence or laboratory reports to local and county health departments, who then forward reports to the state health departments (16). Each week, health departments in 50 states, New York City (a separate reporting jurisdiction from New York State), the District of Columbia, and 5 U.S. territories compile surveillance data from their reporting sites and voluntarily transmit disease incidence data to CDC through the National Electronic Telecommunications System for Surveillance.
Conditions associated with critical biologic agents that were nationally notifiable, reported to NNDSS, and included in this study were anthrax, botulism, brucellosis, cholera, plague, tularemia, and selected viral encephalitides. Botulism is reported as two distinct conditions: foodborne botulism and other or unspecified forms of botulism, including wound botulism. All of the study conditions, except tularemia and selected viral encephalitides, were designated as nationally notifiable throughout the study period. Other than tularemia, only cases reported for those diseases designated as nationally notifiable and from states in which the disease was legally reportable were analyzed. Although tularemia was deleted from the nationally notifiable disease list in 1995 because of decreasing incidence, the disease remained reportable in most states, and the annual number of cases reported to NNDSS remained stable in subsequent years; therefore, tularemia incidence data for the entire study period were included in the analysis.
Incidence rates were calculated for the demographic and geographic descriptors of sex, age (grouped as <1 year, 1–4, 5–14, 15–24, 25–39, 40–64, and >65 years), racial category (American Indian or Alaska Native, Asian or Pacific Islander, black, white, and other), Hispanic ethnicity, and state of residence. Seasonal incidence (spring, summer, fall, and winter) was examined on the basis of data reported with one of three types of dates: onset date, date of diagnosis, or date of laboratory result.
Average annual age-, sex-, race-, ethnicity-, and state-specific disease incidence rates for the period 1992–1999 were estimated by averaging the total annual number of case counts by subcategory, and dividing by the study’s mid-year (1995) U.S. population. St