Lesson 2 - Public Health Surveillance
Lesson 2 - Public Health SurveillanceLesson 2 Objectives:
- 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 SurveillanceSurveillance: Information for Action
The Centers for Disease Control and Prevention have defined surveillance as follows:
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?
~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 DataSources 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.
CDC WONDER
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.
SEER
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]
Health Survey |
Target Population |
Mode/ Sampling Strategy/Size |
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.
Health Survey |
Target Population |
Mode/ Sampling Strategy/Size |
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 http://www.cdc.gov/healthyyouth/sexualbehaviors/index.htm |
- This website provides an Interactive Data Query System for accessing data from the NHIS: https://www.cdc.gov/nchs/nhis/shs.htm
Health Survey |
Target Population |
Mode/ Sampling Strategy/Size |
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 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.
Health Survey |
Target Population |
Mode/ Sampling Strategy/Size |
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 |
Health Survey |
Target Population |
Mode/ Sampling Strategy/Size |
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 DesignEven 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:
Advantages
- Inexpensive
- Relatively quick
- Can help establish or clarify a hypothesis
Disadvantages
- 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.
Each of these approaches is useful, but to what population can the results be generalized?
2.4 - Lesson 2 Summary
2.4 - Lesson 2 SummaryLesson 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.