Lesson 5: Public Health Surveillance

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Answers to Self-Assessment Quiz

  1. A, B, C, D. The term public health surveillance includes data collection, analysis, interpretation, and dissemination to help guide health officials and programs in directing and conducting disease control and prevention activities. However, surveillance does not include control or prevention activities themselves.
  2. A, B, C, D, E. Current public health surveillance targets health-related conditions among humans, including chronic diseases (e.g., cancer), communicable diseases (e.g., those on the notifiable disease list), health-related behaviors, and occupationally related conditions (e.g., black lung disease and other pneumoconioses). Surveillance also focuses on indicators of disease potential (e.g., such diseases among animals as rabies) or presence of an infectious agent among animals or insects (e.g., West Nile virus among mosquitoes).
  3. A. Public health surveillance can be thought of as one of the methods that a community has available to monitor the health among its population by detecting problems, communicating alerts as needed, guiding the appropriate response, and evaluating the effect of the response. Surveillance should not be confused with medical surveillance, which is monitoring of exposed persons to detect early evidence of disease. Public health surveillance is the continued watchfulness for public health problems; it is not a data-collection system.
  4. B (False). The practice of surveillance is not limited to public health agencies. Hospitals, nursing homes, the military, and other institutions have long conducted surveillance of their populations.
  5. A, B, C, D. Among the uses of surveillance are detecting individual cases of diseases of public health importance (e.g., malaria), supporting planning (e.g., priority setting), monitoring trends and patterns of health-related conditions (e.g., elevated blood lead levels), and supporting evaluation of prevention and control measures (e.g., a vaccination requirement).
  6. A, C, D. Data collected through vital registration, disease notifications, and population surveys are commonly used for surveillance of health-related problems. Data from randomized clinical trials typically cover only a specially selected population and are used to answer specific questions about the effectiveness of a particular treatment. They are not useful for surveillance.
  7. B (False). One of the important uses of surveillance data and one of the key reasons to close the surveillance loop by disseminating surveillance data back to health-care providers, is to provide clinically relevant information about disease occurrence, trends, and patterns. For example, health departments alert clinicians to the presence of new diseases (e.g., severe acute respiratory syndrome [SARS]) and provide information so that clinicians can make diagnoses. Health departments also advise clinicians about changing patterns of antibiotic resistance so that clinicians can choose the right treatment regimen.
  8. B. Vital statistics refer to data on birth, death, marriage, and divorce. Therefore, vital statistics are the primary source of data on mortality, but not on morbidity (illness), behaviors, injury (other than fatal injuries), and health-care usage. Before development of population health surveys and disease registries and the use of health-care records to assess morbidity, vital statistics were the primary source of data on the health of populations. During recent years, administrative, financial, and other health-care–related records have supplemented the information from vital statistics, especially for assessing morbidity within populations. National, state, and local population-based health surveys, some of which are conducted on a regular or continuing basis, provide another important part of our view of the health of populations.
  9. A (True). Vital statistics are usually thought of as an archive of births, deaths, marriages, and divorces. Vital statistics offices in health departments typically are not linked to disease prevention and control activities. However, surveillance for certain health problems might rely on vital statistics as its primary source of data. When these data undergo timely and systematic analysis, interpretation, and dissemination with the intent of influencing public health decision-making and action, they become surveillance data.
  10. B, C, D. Sources of morbidity (illness) data include notifiable disease reports, laboratory data, hospital discharge data, outpatient health-care data, and surveillance for specific conditions (e.g., cancer). Vital records are an important source of mortality data, and even though a patient first gets sick from a disease before dying from it, vital records are not regarded as a source of data for the surveillance of morbidity from the disease. Environmental monitoring is used to evaluate disease potential or risk.
  11. B (False). Notifiable disease surveillance targets occurrence or death from any of the diseases on the list.
  12. B. The list of nationally notifiable diseases is compiled by the Council of State and Territorial Epidemiologists (CSTE) and the Centers for Disease Control and Prevention. The list of notifiable diseases that physicians must report to their state or local health department is set by the state, either by the state legislature, the state board of health, the state health department, the state health officer, or the state epidemiologist. CSTE votes on the diseases that should be nationally notifiable, but the states have the ultimate authority whether to add any newly voted diseases to their state list.
  13. A or B, depending on the state. The agency that a physician should notify is determined by the state, just as the list of notifiable diseases is set by the state (see answer to question 12). The manner in which notification should occur and how rapidly reports should be made are also defined by the state and can vary by disease. For example, the state might require that a case of cholera be reported immediately by telephone or fax to the local or state health department, whereas reporting of varicella (chickenpox) might only be required monthly, by using a paper form. Regardless of the disease and reporting requirements, reporting should proceed through established channels. In certain states, physicians should notify the county health department, which will then notify the state health department, which will notify CDC, which will notify the World Health Organization. In states with no or limited local health departments, physicians are usually required to notify the state health department. The seriousness of the disease might influence how rapidly these communications take place but should not influence the sequence.
    1. A. Notifiable disease surveillance is state-based, with subsequent reporting to CDC. Surveillance for consumer product-related injuries is hospital emergency department-based with subsequent reporting to the Consumer Product Safety Commission.
    2. A. Notifiable disease surveillance attempts to identify every case of a notifiable disease. Surveillance for consumer product-related injuries relies on a sample of hospital emergency departments to characterize the incidence and types of these injuries.
    3. C. Because surveillance for notifiable diseases and surveillance for consumer product-related injuries are both ongoing, both can monitor trends over time.
    4. B. Surveillance for consumer product-related injuries is based on a statistically valid sample of hospital emergency departments in the United States. Notifiable disease surveillance covers the entire population.
    5. D. Neither approach to surveillance is perfect. Underreporting is a serious problem in the majority of states for notifiable disease surveillance. Surveillance for consumer product-related injuries is based on visits to a sample of emergency departments; therefore, persons who do not seek care at an emergency department are not represented.
  15. A, B, D. Evaluation of surveillance for a health-related problem should include review of the purpose and objectives of surveillance, the resources needed to conduct surveillance for the problem, and whether the characteristics of well-conducted surveillance are present. Because surveillance does not have direct responsibility for the control of the health problem, this is not part of evaluating a surveillance system. Whether effective measures for preventing or controlling a health-related problem are available can be a useful criterion in prioritizing diseases for surveillance.
  16. A, B, D. The incidence of, public concern about, and social and economic impact of a health problem are all important in assessing its suitability for surveillance. Although previous studies of the problem might have helped to characterize its natural history, cause, and impact, the number of such studies is not used as a criterion for prioritization.
    1. C (Both). Surveillance based on specific case definition for a disease attempts to identify individual cases of disease of public health importance, and syndromic surveillance, depending on its purpose, might also attempt to identify cases of disease of public health importance. In certain situations, the goal of syndromic surveillance might be to identify clusters or outbreaks (more cases than expected) of disease rather than individual cases.
    2. C (Both). Both syndromic surveillance and surveillance based on a specific case definition for a disease can be used to watch for diseases caused by acts of biologic or chemical terrorism. Which approach is used depends on the disease and the setting.
    3. B. Syndromic surveillance that targets sales of over-the-counter medications, calls to hotlines, and school or work absenteeism all watch for disease before a patient seeks care from a health-care provider. Surveillance based on a specific case definition for a disease is usually based on reporting by a health-care provider.
    4. D. Neither type of surveillance can function properly without attention and effort on the part of the health department. Health department staff should review the case report forms and conduct follow-up of cases reported through surveillance based on specific case definitions for diseases. Health department staff should review the cases identified by syndromic surveillance and determine whether they reflect true outbreaks or not. Additionally, health department staff should compile and communicate the results. These tasks are a minimum.
  18. A, B, D, E. Analysis by time often includes comparison with previous weeks and previous years. Analysis by place can include analysis of both numbers and rates. Routine analysis by person includes age and sex, but a three-variable table of age by race and sex is probably too much stratification for routine analysis.
  19. A, B, C, D, E. An increase in case reports during a single week might represent a true increase in disease (i.e., an outbreak). However, the increase can also represent an increase in the population (e.g., from an influx of tourists, migrant workers, refugees, or students); reporting of cases in a batch, particularly after a holiday season; duplicate reports of the same case; laboratory or computer error; a new clinic or health-care provider that is more likely to make a particular diagnosis or is more conscientious about reporting; or other sudden changes in the method of conducting surveillance.
  20. B. The primary purpose of preparing and distributing surveillance summaries is to provide timely information about disease occurrence to those in the community who need to know. The report also serves to motivate those who report by demonstrating that their efforts are valued and to inform health-care providers and others in the community about health department activities and general public health concerns.
    1. B. Sensitivity is the ability of surveillance (or laboratory tests or case definitions) to detect a true case (or, for certain systems, a true outbreak). Specificity is the ability of surveillance (or laboratory tests or case definitions) to rule out disease among persons who do not have it.
    2. A. Predictive value positive is the proportion of patients (or outbreaks) detected by surveillance who truly have the disease (or are true outbreaks). Predictive value positive is a function of both the sensitivity of surveillance and the prevalence of the disease (or prevalence of real outbreaks).
  22. B (False). Underreporting is a serious problem for surveillance that relies on notifications. Because the notifiable disease surveillance is supposed to identify individual cases of disease of public health importance, underreporting of even a single case of, for example, hepatitis A in a food handler, can result in an outbreak that should have been prevented. Similarly, if a limited number of cases are reported at all, even outbreaks can be missed.
  23. B, D. Initiating surveillance for a health-related problem can be justified for multiple reasons. These reasons include if a disease is new and surveillance is the most effective means for collecting information on cases to learn more about its clinical and epidemiologic features (e.g., SARS); if a new prevention or control measure is about to be implemented and surveillance is the most effective means for assessing its impact (e.g., varicella vaccination regulations); or if surveillance is needed to guide, monitor, and evaluate prevention or control measures. Surveillance is more difficult to justify if a disease does not occur locally, even if it is a communicable disease with a high case fatality rate (e.g., Ebola or Marburg virus infection), or simply because CDC requests it (without funding).
  24. B (False). A case definition for surveillance should be clear, understandable, acceptable, and implementable by those who are required to apply it. However, it need not use the same criteria that are used for clinical purposes. For example, health-care providers might treat patients on the basis of clinical features without laboratory confirmation, whereas a surveillance case definition might require confirmation, or vice versa.
  25. C. The most important way to improve notifiable disease surveillance is to ensure that everyone who is supposed to report knows
    • that they are supposed to report,
    • what to report (i.e., which diseases are on the list), and
    • how, to whom, and how quickly to report.

    In addition, they will be more likely to report if they know that the health department is actually doing something with the reports. No data are available that demonstrate that reporting through the Internet improves reporting; in fact, for certain health-care providers, reporting might involve extra work. Requiring more disease-specific forms tends to reduce reporting, because it requires more time and effort for those reporting. Reducing the number of diseases on the list might be part of a strategy to improve reporting, but it is not the most important way to do so.

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