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State and local public health officials rely on health-care providers, laboratories, and other public health personnel to report the occurrence of notifiable diseases to state and local health departments. Without such data, unusual occurrences of diseases might not be detected, trends cannot be accurately monitored, and the effectiveness of intervention activities cannot be easily evaluated.
In the United States, requirements for reporting diseases are mandated by state or local laws or regulations, and the list of reportable diseases in each state differs. CDC and the Council of State and Territorial Epidemiologists (CSTE) have established a policy that requires state health departments to report cases of selected diseases (Table 1) to CDC's National Notifiable Diseases Surveillance System (NNDSS) (1,2). However, before 1990, the usefulness of such data was limited by the lack of uniform case definitions for public health surveillance. Without explicit criteria for identifying cases for public health surveillance purposes, state health departments and individual practitioners often applied different criteria for reporting similar cases (3).
In October 1990, in collaboration with CSTE, CDC published Case Definitions for Public Health Surveillance (4), which, for the first time, provided uniform criteria for reporting cases to increase the specificity of reporting and improve the comparability of diseases reported from different geographic areas. This web-based document supersedes the “1990 Report”(MMWR 1990; 39[No.RR-13]), which included infectious diseases and one noninfectious condition (i.e., spinal cord injury) and the “1997 Report”entitled Case Definitions for Infectious Conditions Under Public Health Surveillance (MMWR 1997;46 [No. RR-10]) and provides updated uniform criteria for public health professionals to use when reporting the nationally notifiable infectious diseases. A revision date is included for each case definition that has been revised. Newly generated case definitions that have not been previously published are designated as “adopted”on the specified date. The CDC Surveillance Coordination Group has established a steering committee that is charged with the development of a broad range of case definitions for noninfectious conditions (e.g., environmental or occupational conditions, chronic diseases, adverse reproductive health events, and injuries).
Data for nationally notifiable diseases reported by the 50 states, New York City, the District of Columbia, and the U.S. territories are collated and published weekly in the Morbidity and Mortality Weekly Report (MMWR). Cases reported by state health departments to the NNDSS for weekly publication are provisional because of ongoing revision of information and delayed reporting; thus, these numbers may change. Updated final reports are published annually in CDC's Summary of Notifiable Diseases, United States (1).
The CDC/CSTE surveillance case definitions included in this report differ in their use of clinical, laboratory, and epidemiologic criteria to define cases. Some clinical syndromes do not have confirmatory laboratory tests; however, laboratory evidence may be one component of a clinical definition (e.g., toxic-shock syndrome). Most case definitions include a brief clinical description; however, unless this description is explicitly cited in the case classification section, it is included only as background information.
Some diseases require laboratory confirmation for diagnosis regardless of clinical symptoms, whereas others are diagnosed based on epidemiologic data. Many case definitions for the childhood vaccine-preventable diseases and foodborne diseases include epidemiologic criteria (e.g., exposure to probable or confirmed cases of disease or to a point source of infection [i.e., a single source of infection, such as an event resulting in a foodborne-disease outbreak, to which all confirmed case-patients were exposed]). In some instances, the anatomic site of infection may be important; for example, respiratory diphtheria is notifiable, whereas cutaneous diphtheria is not.
Substantial amounts of information, including results of laboratory tests, must be collected for many diseases before a final case classification is possible. State health departments should continue prompt reporting of provisional cases to CDC, and records should be updated with the appropriate classification status when additional surveillance information becomes available. Cases should be categorized as laboratory-confirmed (a subset of all confirmed cases) only if they meet the laboratory criteria specified. For additional information about procedures for reporting diseases to CDC, see the Manual of Procedures for the Reporting of Nationally Notifiable Diseases to CDC (5). Requests for this manual should be sent to the following e-mail address: soib@cdc.gov
Case definitions for some infectious conditions not considered nationally notifiable also are included on this web site. Some of these conditions may have been nationally reportable or may become so; definitions are included here to facilitate interpretation of data for these diseases. State health departments also provide CDC with information regarding certain conditions of public health interest, whether nationally reportable, through supplementary surveillance systems that collect more detailed, condition-specific information (5).
The usefulness of public health surveillance data depends on its uniformity, simplicity, and timeliness. The case definitions contained in the "1997 Report" establish uniform criteria for disease reporting and should not be used as the sole criteria for establishing clinical diagnoses, determining the standard of care necessary for a particular patient, setting guidelines for quality assurance, or providing standards for reimbursement. Use of additional clinical, epidemiologic, and laboratory data may enable a physician to diagnose a disease even though the formal surveillance case definition may not be met.
The list of nationally reportable infectious diseases changes periodically. Diseases may be added to the list as new pathogens emerge or deleted as their incidence declines. Public health officials at state health departments and CDC collaborate in determining which diseases should be nationally notifiable; CSTE, in conjunction with CDC, makes recommendations annually for additions and deletions to the list of nationally notifiable diseases (1,2). As knowledge increases and diagnostic technology improves, some definitions will change to reflect those trends. Thus, future revisions can be expected. Future changes to the case definitions for nationally notifiable infectious diseases will be made available on this web site.
These case definitions are to be used for identifying and classifying cases, both of which are often done retrospectively, for national reporting purposes. They should not be used as criteria for public health action. For many conditions of public health importance, action to contain disease should be initiated as soon as a problem is identified; in many circumstances, appropriate public health action should be undertaken even though insufficient information is available to determine whether cases meet the case definition.
1. CDC. Summary of notifiable diseases, United States, 1999. MMWR 1999;48(No. 53).
2. Koo D, Wetterhall SF. History and current status of the National Notifiable Diseases Surveillance System. Journal of Public Health Management Practice 1996;2:4-10.
3. Sacks JJ. Utilization of case definitions and laboratory reporting in the surveillance of notifiable communicable diseases in the United States. Am J Public Health 1985;75:1420-2.
4. CDC. Case definitions for public health surveillance, 1990. MMWR 1990;39(No. RR-13).
5. CDC. Manual of procedures for the reporting of nationally notifiable diseases to CDC. Atlanta: US Department of Health and Human Services, Public Health Service, CDC, 1995
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