Public health surveillance of noninfectious conditions and disease outbreaks at the local, state, and territorial levels protects the public’s health by ensuring the proper identification of conditions and health hazards. With these data, local public health officials monitor trends in these conditions, identify populations or geographic areas at high risk, plan prevention and control policies and other interventions, allocate resources effectively, coordinate activities, and assess the effectiveness of their efforts. Local, state, and territorial health departments also use these data to assist the federal government in meeting requirements under the International Health Regulations to identify, respond to, and share information about adverse health events that might constitute a Public Health Emergency of International Concern (PHEIC).
Completeness and Surveillance System Characteristics
Although the sources of data for national notifiable infectious diseases and for national notifiable noninfectious conditions and disease outbreaks are the same (i.e., local, state, and territorial jurisdictions’ data on reportable conditions) and have the same general purpose (i.e., monitoring and responding to the condition to improve population health), there are a number of differences that should be considered when comparing findings across conditions and by time, location, and demographic characteristic. Under-reporting of noninfectious conditions and disease outbreaks to local and state health departments occurs, and the completeness of reporting, and therefore of notifications to CDC, varies by condition. Moreover, variations in data collection methods also influence comparative observations across conditions and disease outbreaks. For example, case-based surveillance of acute pesticide-related illness or injury, elevated blood lead levels, and cancer is focused on collecting information on cases that meet the criteria specified in national condition-specific case definitions and on collecting information about those persons’ conditions. In contrast, surveillance of outbreaks of foodborne and waterborne illness seeks to identify clusters of sick persons with a common exposure (as opposed to persons with a specific disease). Foodborne disease outbreaks are defined as two or more cases of similar illness resulting from common ingestion of a food. Waterborne disease outbreaks are defined as two or more cases of a similar illness resulting from common exposure to water or water-associated chemicals. For these conditions, information is collected about the characteristics of the disease outbreaks, including data from epidemiologic and environmental investigations.
Even among conditions for which case-based surveillance methods are used, there is substantial variation in what a condition means. For example, for a condition such as elevated blood lead levels, surveillance uses laboratory findings to identify persons who have been exposed to a hazard, but does not require a clinical diagnosis of lead poisoning. In contrast, for many other conditions, a diagnosis based on clinical and/or pathological criteria is needed to meet the case definition for a notification to CDC.
The meaning of the date of the occurrence of the condition also varies among the conditions and across jurisdictions. For cancer, as for some infectious diseases, including tuberculosis and human immunodeficiency virus infection diagnosis, date of occurrence is assigned based on the date the condition is diagnosed. For silicosis, date of occurrence represents the date of the initial report (e.g., the date of a hospital discharge report, clinician report, or a workers’ compensation claim). For lead screening test results, date of occurrence is the date the sample was tested. For acute pesticide-related illness, it is the date of pesticide exposure, which is generally identical to the date of symptom onset since symptom onset is within seconds to hours of exposure. For disease outbreaks, date of occurrence represents date of the illness onset of the first case in the outbreak.
The source and definitions of race and ethnicity also vary over time and among conditions. For example, information about race and ethnicity for lead exposure is based on self-report. Whereas for cancer incidence it is based on medical records, which might or might not be based on self-report, or from matching the names of persons with cancer with lists of surnames for different ethnic groups or with tribal registries. For silicosis, race and ethnicity are based on self-report, report from next-of-kin, or from medical records. Race- and ethnicity-specific information among the conditions might also vary depending on the jurisdictions’ systems for submitting notifications to CDC and the need to protect private health information. There are also variations across conditions in terms of which specific U.S. Census Bureau data sets were used to calculate rates of occurrence of the conditions.