Lesson 2 - Public Health Surveillance

Lesson 2 - Public Health Surveillance

Lesson 2 Objectives:

Upon completion of this lesson, you should be able to:

  • State at least 5 uses of disease surveillance information.
  • Explore some public sources of disease surveillance data.
  • Compare and contrast 5 health surveys conducted in the US with regard to the target population, sampling strategy, and purpose
  • Identify advantages and disadvantages of surveys
  • Differentiate between sampling strategies in order to select an appropriate sampling scheme for a survey

2.1 - Public Health Surveillance

2.1 - Public Health Surveillance

Surveillance: Information for Action

The Centers for Disease Control and Prevention have defined surveillance as follows:

"the ongoing systematic collection, analysis, and interpretation of data essential to the planning, implementation, and evaluation of public health practice, closely integrated with the timely dissemination of these data to those responsible for prevention and control ."

Disease surveillance is the basic process by which epidemiologists answer questions about who, where, and when.

Who is getting the disease? Are there differences in the rates of disease by age? sex? race?

Where is the disease happening? Are there geographic areas with particularly high rates? extremely low rates?

Is the occurrence of the disease changing over time? Is the disease becoming more frequent? less frequent?

“Good surveillance does not necessarily ensure the making of right decisions, but it reduces the chance of wrong ones."

~Alexander D. Langmuir NEJM 1963;268;182-191.

Disease surveillance information is useful for:

  • Estimating the magnitude of a problem
  • Determining the geographic distribution of illness
  • Portraying the natural history of a disease
  • Detecting epidemics or defining a problem
  • Generating hypotheses, stimulating research
  • Evaluating control measures
  • Monitoring changes in infectious agents
  • Detecting changes in health practices
  • Facilitating planning

Evaluation of Surveillance Systems

A disease surveillance system should be simple, flexible, and acceptable to the population. For example, to detect hunting-related shooting injuries, the requirements for a hunter to report an episode should not be onerous or many shooting injuries will go unrecorded. The surveillance system should also be representative of the population and provide a timely alarm. Like a smoke detector without a power source, a surveillance system that is not able to recognize a disease outbreak quickly and accurately is not very useful.

2.2 - Sources of Public Health Surveillance Data

2.2 - Sources of Public Health Surveillance Data

Sources of public health surveillance data can include:

  • notifiable diseases,
  • vital records (e.g. National Infant Mortality Surveillance, birth, death records),
  • registry and survey data,
  • administrative databases (such as Medicare or a prescription database), and
  • some laboratory records.

Below are some websites to explore available sources of public health data:

Integrated Surveillance Information Systems/National Electronic Disease Surveillance System
In the U.S., this has been developed to standardize health reporting and link laboratory, hospital, and managed care data.

Pennsylvania’s Department of Health Vital Records

Enterprise Data Dissemination Informatics Exchange (EDDIE)
This is an interactive health statistics dissemination web tool where you can create customized data tables, charts and maps for various health related data.
This organization furthers the CDC's mission of health promotion and disease prevention by speeding and simplifying access to public health information for state and local health departments, the Public Health Service, and the academic public health community.

Surveillance, Epidemiology, and End Results Program of the National Cancer Institute

The SRTR Database
The Scientific Registry of Transplant Recipients

U.S. Fire Administration (USFA)
The USFA collects data from a variety of sources to provide information and analyses on the status and scope of the fire problem in the United States.

Health Surveys

In the US, governmental agencies conduct surveys for various purposes at regular intervals. Investigate these surveys by following the links below. [Select to expand]

The Behavioral Risk Factor Surveillance System (BRFSS) is the nation’s premier system of health-related telephone surveys that collect state data about U.S. residents regarding their health-related risk behaviors, chronic health conditions, and use of preventive services. Established in 1984 with 15 states, BRFSS now collects data in all 50 states as well as the District of Columbia and three U.S. territories. BRFSS completes more than 400,000 adult interviews each year, making it the largest continuously conducted health survey system in the world.
Mode/ Sampling
Health Issues;
Example of a Disease/ Outcome and an Exposure
BRFSS Non-institutionalized adult residents of the 50 states and the District of Columbia and selected territories

Mode: telephone (cell and landline) survey

Sampling strategy: Random-digit dial with post-stratification

weighting Size: 400,000+ each year

Health-related risk behaviors and events, chronic health conditions, use of preventive services, emerging health issues (e.g. vaccine shortage, influenza-like illnesses) Example: 2012, Number of adults age 50+ Who Had Blood Stool Test Screening within Last Two Years for Colorectal Cancer 38.8% Yes(CI 31.7-45.9, n=208) No 61.2% (CI 54.1-68.3, n=308) http://apps.nccd.cdc.gov/brfsssmart/MMSARiskChart.as p?yr=2012&MMSA=281&c at=CC&qkey=8521&grp=0

The Youth Risk Behavior Surveillance System (YRBSS) monitors six categories of health-related behaviors that contribute to the leading causes of death and disability among youth and adults, including—

  • Behaviors that contribute to unintentional injuries and violence
  • Sexual behaviors related to unintended pregnancy and sexually transmitted diseases, including HIV infection
  • Alcohol and other drug use
  • Tobacco use
  • Unhealthy dietary behaviors
  • Inadequate physical activity

YRBSS also measures the prevalence of obesity and asthma and other health-related behaviors plus sexual identity and sex of sexual contacts.

YRBSS is a system of surveys. It includes 1) a national school-based survey conducted by CDC and state, territorial, tribal, and 2) local surveys conducted by state, territorial, and local education and health agencies and tribal governments.

Mode/ Sampling
Health Issues;
Example of a Disease/ Outcome and an Exposure
YRBSS Students in public and private high school (9th-12th grade) at the national, state, and local levels in the U.S.

Mode: Anonymous, school-based questionnaire survey, administered in odd-numbered years.

Sampling strategy: multi-stage cluster design.

Size: In 2013, 13,000 youth in 42 states, 21 large urban schools, some tribal governments

Behaviors that contribute to unintentional injuries and violence, Sexual behaviors that contribute to unintended pregnancy and sexually transmitted diseases, including HIV infection, Alcohol, and other drug use, Tobacco use, Unhealthy dietary behaviors, Inadequate physical activity, obesity, and asthma Example: among U.S. high school students surveyed in 2013146.8% had ever had sexual intercourse 34.0% had had sexual intercourse during the previous 3 months, and, of this 40.9% did not use a condom the last time they had sex 15.0% had had sex with four or more people during their life
The National Health Interview Survey (NHIS) has monitored the health of the nation since 1957. NHIS data on a broad range of health topics are collected through personal household interviews. Survey results have been instrumental in providing data to track health status, health care access, and progress toward achieving national health objectives.
Mode/ Sampling
Health Issues;
Example of a Disease/ Outcome and an Exposure
NHIS Noninstitutionalized civilian adult population residing in the United States

Mode: Cross-sectional household interview survey

Sampling Strategy: stratified multistage household sample, with oversampling of elderly and minorities.

Size: 30,000-40,000 households per year (75,000-100,000 persons)

Monitor trends in illness and disability, track progress toward achieving national health objectives, epidemiologic and policy analysis of such timely issues as characterizing those with various health problems, determining barriers to accessing and using appropriate health care, and evaluating Federal health programs. Example: In 2012 the NHIS showed that 18% percent of U.S. adults were current smokers and 21% were former smokers http://www.cdc.gov/nchs/ data/series/sr_10/sr10_26 0.pdf
The National Health and Nutrition Examination Survey (NHANES) is a program of studies designed to assess the health and nutritional status of adults and children in the United States. The survey is unique in that it combines interviews and physical examinations. NHANES is a major program of the National Center for Health Statistics (NCHS). NCHS is part of the Centers for Disease Control and Prevention (CDC) and has the responsibility for producing vital and health statistics for the Nation.

The NHANES program began in the early 1960s and has been conducted as a series of surveys focusing on different population groups or health topics. In 1999, the survey became a continuous program that has a changing focus on a variety of health and nutrition measurements to meet emerging needs. The survey examines a nationally representative sample of about 5,000 persons each year. These persons are located in counties across the country, 15 of which are visited each year.

The NHANES interview includes demographic, socioeconomic, dietary, and health-related questions. The examination component consists of medical, dental, and physiological measurements, as well as laboratory tests administered by highly trained medical personnel.

Findings from this survey will be used to determine the prevalence of major diseases and risk factors for diseases. Information will be used to assess nutritional status and its association with health promotion and disease prevention. NHANES findings are also the basis for national standards for such measurements as height, weight, and blood pressure. Data from this survey will be used in epidemiological studies and health sciences research, which help develop sound public health policy, direct and design health programs and services, and expand the health knowledge for the Nation.

Mode/ Sampling
Health Issues;
Example of a Disease/ Outcome and an Exposure
NHANES Non-institutionalized adults and children in U.S.

Mode: Face-to-face interviews and clinical examinations.

Sampling strategy: Multistage area probability sampling.

Size: 5,000 persons each year.

Determine the prevalence of major diseases and risk factors for diseases assess nutritional status and its association with health promotion and disease prevention. Establishes the basis for national standards for such measurements as height, weight, and blood pressure. Example: During 2007– 2012, 46.2% of adults aged 40–79 with lung obstruction currently smoked cigarettes. About 41% with mild and 55% with moderate or worse obstruction were current smokers. http://www.cdc.gov/nchs/ data/databriefs/db181.html
The California Health Interview Survey (CHIS) is the largest state health survey in the nation. It is a web and telephone survey that asks questions on a wide range of health topics. CHIS is conducted on a continuous basis allowing the survey to generate timely one-year estimates. CHIS provides representative data on all 58 counties in California and provides a detailed picture of the health and healthcare needs of California’s large and diverse population.
Mode/ Sampling
Health Issues;
Example of a Disease/ Outcome and an Exposure
CHIS Non-institutionalized civilian population of California (adults, teenagers and children)

Mode: Telephone (cell phones and land-lines) survey

Sampling strategy: random-digit-dial with a supplemental surname list frame for Korean and Vietnamese populations.

Size: 42,000-50,000

From asthma, diabetes, and obesity to immigrant health and health insurance coverage, CHIS covers dozens of essential health topics. Example: Projections from the California Simulation of Insurance Markets (CalSIM) model indicate that up to half of Californians remaining uninsured will be undocumented immigrants who are not eligible under the Affordable Care Act (ACA). Most others lacking insurance will be eligible for Medi-Cal or subsidized insurance through Covered California but remain unenrolled due to difficulties with the enrollment process, inability to afford coverage, concerns about negative immigration-related consequences for themselves or their family members, or other barriers. Almost three/fourths of the remaining uninsured will be Latino, almost one-third will reside in Los Angeles County, and about 70 percent will CHIS is conducted by the UCLA Center for Health Policy Research in collaboration with the California Department of Public Health and the Department of Health Care Services be exempt from paying a tax penalty for lacking coverage. http://healthpolicy.ucla.edu /chis/research/Pages/default.aspx

2.3 - Survey & Sampling Design

2.3 - Survey & Sampling Design

Even though this is not a course on survey design, a large source of public health data comes from surveys. As we saw earlier in the course, it is often not feasible to take measurements on the entire target population, so we must select a sample in which to gather data. This section introduces some advantages and disadvantages of using surveys and approaches to drawing a sample for an epidemiologic survey.

Survey Studies

An epidemiologic survey consists of a simultaneous assessment of the health outcome and exposures as well as potential confounders and effect modifiers. A survey given at a single time point can be part of a cross-sectional study. Some epidemiologists may call it a prevalence study. The survey results provide a 'snapshot' of a population. Surveys are a useful tool for gauging the health of a population or monitoring the effectiveness of a preventative intervention or provision of emergency relief.  

While a survey may provide a relatively quick and inexpensive method for assessing the health of a population, there are both pros and cons, as noted below:


  • Inexpensive
  • Relatively quick
  • Can help establish or clarify a hypothesis


  • Exposure may not have preceded disease or outcome. This limits the assessment of causality. For example, a survey may ask about the current behavior of smoking and a diagnosis of asthma. While the results may show an association between smoking and asthma, we may not be able to accurately determine which came first.
  • Disease and health outcomes with a long duration can be over-represented. Less severe outcomes may be under-represented because they may not have been diagnosed at the time of the survey.
  • Surveys are subject to information bias (e.g. from inaccurate recall or misdiagnosis) and selection bias (e.g. those without a telephone cannot be selected for a random digit dial survey)

Survey Questions and Administration

Survey questions are carefully structured in order to reduce bias. Care should be given to the wording and order of questions. Using a standard questionnaire increases the reliability and validity of the results. A reliable survey has internal consistency and produces results that are replicable. The subject would answer the question in the same way if asked again. Valid questions are those which accurately assess the specific concept that is being measured.

The process of administering a survey should be standardized to reduce the potential for bias. The respondent should be informed of the purpose of the research and freely consent to participate. A survey with a low response rate is likely to have some bias.

STAT 507 is a course in epidemiologic research methods so we will not delve into the strengths and weaknesses of various methods for evaluating the reliability and validity of a survey instrument as might be presented in a psychometric course. You should however recognize the need to consider this type of analysis when selecting a survey instrument.

Sampling Designs

These methods of sampling can be applied to survey studies, as well as other observational and interventional studies.

First, if the population can be enumerated (listed), a simple random sampling approach can be used to draw a representative sample of potential participants. For example, you might generate a list of all children attending a public school and then from this list, randomly select students for the survey. Procedures for simple random sampling can be done in many software packages, including Excel. The use of simple sampling allows us to generalize the results of the survey back to the population from which the sample was drawn.
Sometimes, we want to make sure that there are an adequate number of responses from a group that is relatively small. To do that, we might use stratified random sampling which divides groups into homogeneous groups. Then we can draw simple random samples from each of the groups. Stratified sampling assures that selected subgroups of the population will be represented in the sample. If the strata are homogeneous, statistical precision from stratified sampling is greater than that achieved with simple random sampling. Stratified samples can be proportionate (or disproportionate) to the size of the stratum. If sampling is disproportionate, overall population estimates are constructed by weighting within-group estimates by the sampling fraction. Cluster sampling is a specific type of stratified sampling, and often refers to sampling from geographic areas. A cluster might be a zip code area in the US or streets within a city.
Systematic sampling occurs when we select our sample in a systemic manner. For example, you might select every 10th house on a street to participate in a household survey. Systematic sampling can be easier to implement than simple random sampling and may represent the population as well as a simple random sample. However, if every rth unit corresponds to an existing sequence in the population with the result that each member of the sample was selected from the same part of the recurring pattern, the sample will be biased. For example, if an observation is made every seventh day, beginning on a Monday, the entire sample will only represent Monday experiences.
Finally, there are several types of surveys that may be used but may produce biased population estimates. First, we may choose a convenience sample, such as randomly asking people on a street corner or in a store to participate in a survey. The convenience sample may be useful in gathering preliminary or pilot data for a future survey that would be larger and have more rigorous sampling methods. Finally, you may choose purposive sampling because you are particularly interested in the responses of a specific group.

Each of these approaches is useful, but to what population can the results be generalized? 

2.4 - Lesson 2 Summary

2.4 - Lesson 2 Summary

Lesson 2 Summary

Public health surveillance is important for the health of any nation. In order to decide how to allocate resources, it is vital to know who is being affected, where those people live, and the timeliness of the issue. There are many sources of public health data that can be used to achieve these goals including vital records, mandatory reporting, registries, and health surveys. Surveys are used to gather information that is not standardly or systematically collected. Since we often cannot gather data on the entire population of interest, we need to select a subgroup to sample from, and different methods for sampling were outlined in this lesson.

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