Other Person- or Disease-Related Risk Factor
Other Person- or Disease-Related Risk Factor
For certain diseases, information on other specific risk factors (e.g., race, ethnicity, and occupation) are routinely collected and regularly analyzed. For example, have any of the reported cases of hepatitis A occurred among food-handlers who might expose (or might have exposed) unsuspecting patrons? For hepatitis B case reports, have two or more reports listed the same dentist as a potential source? For a varicella (chickenpox) case report, had the patient been vaccinated? Analysis of risk-factor data can provide information useful for disease control and prevention. Unfortunately, data regarding risk factors are often not available for analysis, particularly if a generic form (i.e., one report form for all diseases) or a secondary data source is used.
Interpreting results of analyses When the incidence of a disease increases or its pattern among a
specific population at a particular time and place varies from its expected pattern, further investigation or increased emphasis on prevention or control measures is usually indicated. The amount of increase or variation required for action is usually determined locally and reflects the priorities assigned to different diseases, the specific population at a particular time and place varies from its expected pattern, further investigation or increased emphasis on prevention or control measures is usually indicated. The amount of increase or variation required for action is usually determined locally and reflects the priorities assigned to different diseases, the
For certain diseases (e.g., botulism), a single case of an illness of public health importance or suspicion of a common source of infection for two or more cases is often sufficient reason for initiating an investigation. Suspicion might also be aroused from finding that patients have something in common (e.g., place of residence, school, occupation, racial/ethnic background, or time of onset of illness). Or a physician or other knowledgeable person might report that multiple current or recent cases of the same disease have been observed and are suspected of being related (e.g., a report of multiple cases of hepatitis A within the past 2 weeks from one county).
Observed increases or decreases in incidence or prevalence might, however, be the result of an aspect of the way in which surveillance was conducted rather than a true change in disease
occurrence. Common causes of such artifactual changes are: • Changes in local reporting procedures or policies (e.g., a change from passive to active surveillance). • Changes in case definition (e.g., AIDS in 1993).
• Increased health-seeking behavior (e.g., media publicity prompts persons with symptoms to seek medical care).
• Increase in diagnosis. • New laboratory test or diagnostic procedure. • Increased physician awareness of the condition, or a new
physician is in town. • Increase in reporting (i.e., improved awareness of requirement
to report). • Outbreak of similar disease, misdiagnosed as disease of interest. • Laboratory error.
• Batch reporting in which reports from previous periods are held
and reported all at once during another reporting period (e.g., reporting all cases received during December and the first week of January during the second week of January).
Artifactual changes include an increase in population size, improved diagnostic procedures, enhanced reporting, and duplicate reporting. Compare the sharp increases in disease incidence illustrated in Figures 5.7 and 5.8. Although they appear similar, the increase displayed in Figure 5.7 represents a true increase in incidence, whereas the increase displayed in Figure 5.8 resulted
from a change in the case definition. 22,23 Nonetheless, because a health department’s primary responsibility is to protect the health
of the public, public health officials usually consider an apparent increase real, and respond accordingly, until proven otherwise.
Figure 5.7 Reported Cases of Salmonellosis per Figure 5.8 Reported Cases of AIDS, by Year — 100,000 Population, By Year — United States,
United States* and U.S. Territories, 1982– 1972–2002
2002
* Total number of AIDS cases includes all cases reported to Source: Centers for Disease Control and Prevention.
CDC as of December 31, 2002. Total includes cases among Summary of notifiable diseases–United States, 2002.
residents in the U.S. territories and 94 cases among persons Published April 30, 2004, for MMWR 2002;51(No. 53): p. 59.
with unknown state of residence.
Source: Centers for Disease Control and Prevention. Summary of notifiable diseases–United States, 2002. Published April 30, 2004, for MMWR 2002;51(No. 53): p. 59.
Exercise 5.4
During the previous 6 years, one to three cases per year of tuberculosis had been reported to a state health department. During the past 3 months,
17 cases have been reported. All but two of these cases have been reported from one county. The local newspaper published an article about one of the first reported cases, which occurred in a girl aged 3 years. Describe the possible causes of the increase in reported cases.
Check your answers on page 5-60
Disseminating Data and Interpretations
As Langmuir emphasized, the timely, regular dissemination of
basic data and their interpretations is a critical component of surveillance. Data and interpretations should be sent to those who
“Development of a
provided reports or other data (e.g., health-care providers and
reasonably effective
laboratory directors). They should also be sent to those who use
primary surveillance
them for planning or managing control programs, administrative
system took time. Usually,
purposes, or other health-related decision-making.
2 full years were required. Experience showed that
development was best
Dissemination of surveillance information can take different forms.
achieved by establishing
Perhaps the most common is a surveillance report or summary,
for each administrative unit of perhaps 2–5 million
which serves two purposes: to inform and to motivate. Information
on the occurrence of health problems by time, place, and person
population, a surveillance
team of perhaps two to
informs local physicians about their risk for their encountering the
four persons with
problem among their patients. Other useful information
transport. Each team, in addition to its other duties
accompanying surveillance data might include prevention and
in outbreak containment,
control strategies and summaries of investigations or other studies
visited each reporting unit
of the health problem. A report should be prepared on a regular
regularly to explain and
basis and distributed by mail or e-mail and posted on the health
discuss the program, to distribute forms (and often
department’s Internet or intranet site, as appropriate. Increasingly,
vaccine), and to check on
surveillance data are available in a form that can be queried by the
those who were delinquent
general public on health departments’ Internet sites. 24
in reporting. Regularly distributed surveillance
A surveillance report can also be a strong motivational factor in
reports also helped to
motivate these units.
that it demonstrates that the health department actually looks at the
Undoubtedly, the greatest
case reports that are submitted and acts on those reports. Such
stimulus to reporting was the prompt visit of the
efforts are important in maintaining a spirit of collaboration among
the public health and medical communities, which in turn,
surveillance team for
outbreak investigations
improves the reporting of diseases to health authorities.
and control whenever cases were reported. This simple, obvious, and direct
State and local health departments often publish a weekly or
indication that the routine
monthly newsletter that is distributed to the local medical and
weekly reports were
public health community. These newsletters usually provide tables
actually seen and were a cause for public health
of current surveillance data (e.g., the number of cases of disease
identified since the last report for each disease and geographic area
action did more, I am
sure, than the multitude of
under surveillance), the number of cases previously identified (for
government directives
comparison with current numbers), and other relevant information.
which were issued.”
[Emphasis added] 25 They also usually contain information of current interest about the prevention, diagnosis, and treatment of selected diseases and
summarize current or recently completed epidemiologic investigations.
At the national level, CDC provides similar information through the MMWR, MMWR Annual Summary of Notifiable Diseases, MMWR Surveillance Summaries, and individual surveillance At the national level, CDC provides similar information through the MMWR, MMWR Annual Summary of Notifiable Diseases, MMWR Surveillance Summaries, and individual surveillance
When faced with a health problem of immediate public concern, whether it is a rapid increase in the number of heroin-related deaths in a city or the appearance of a new disease (e.g., AIDS in the early 1980s or West Nile Virus in the United States in 1999), a health department might need to disseminate information more quickly and to a wider audience than is possible with routine reports, summaries, or newsletters. Following the appearance of West Nile Virus in New York City in late August 1999, the following measures were taken:
“Emergency telephone hotlines were established in New York City on September 3 and in Westchester County on September 21 to address public inquiries about the encephalitis outbreak and pesticide application. As of September 28, approximately 130,000 calls [had] been received by the New York City hotline and 12,000 by the WCDH [Westchester County Health Department] hotline. Approximately 300,000 cans of DEET-based mosquito repellant were distributed citywide through local firehouses, and 750,000 public health leaflets were distributed with information about personal protection against mosquito bites. Recurring public messages were announced on radio, television, on the New York City and WCDH World-Wide Web sites, and in newspapers, urging personal protection against mosquito bites, including limiting outdoor activity during peak hours of mosquito activity, wearing long-sleeved shirts and long pants, using DEET-based insect repellents, and eliminating any potential mosquito breeding niches. Spraying schedules also were publicized with recommendations for persons to remain indoors while spraying occurred
to reduce pesticide exposure.”
Depending on the circumstances, reports of surveillance data and their interpretation might also be directed at the general public, particularly when a need exists for a public response to a particular problem.
Exercise 5.5
You have recently been hired by a state health department to direct surveillance activities for notifiable diseases, among other tasks. All
notifiable disease surveillance data are entered and stored in computer files at the state and transmitted to CDC once each week. CDC publishes these data for all states in the MMWR each week, but health department staff do not routinely review these data in the MMWR. The state has never generated its own set of tables for analysis and dissemination, and you believe that it would be valuable to do so to educate and increase interest among health department staff.
1. What three tables might you want to generate by computer each week for use by health department staff?
2. You next decide that it would be a good idea to share these data with health-care providers, as well. What tables or figures might you generate for distribution to health-care providers, and how frequently would you distribute them?
Check your answers on page 5-61
Exercise 5.6
Last week, the state public health laboratory diagnosed rabies among four raccoons that had been captured in a wooded residential neighborhood.
This information will be duly reported in the tables of the monthly state health department newsletter. Who needs to know this information?
Check your answers on page 5-62
Evaluating and Improving Surveillance
Surveillance for a disease or other health-related problem should
be evaluated periodically to ensure that it is serving a useful public health function and is meeting its objectives. Such an evaluation: (1) identifies elements of surveillance that should be enhanced to improve its attributes, (2) assesses how surveillance findings affect control efforts, and (3) improves the quality of data and interpretations provided by surveillance.
Although the aspects of surveillance that are emphasized in an evaluation can differ, depending on the purpose and objectives of surveillance, the evaluation’s overall scope and approach should be similar for any health-related problem. The evaluation usually begins by identifying and interviewing key stakeholders and by collecting background documents, forms, and reports. The evaluation should address the purpose of surveillance, objectives, and mechanics of conducting surveillance; the resources needed to conduct surveillance; the usefulness of surveillance; and the presence or absence of the characteristics or qualities of optimal surveillance. The outcome of the evaluation should provide
recommendations for improvement. 9,27,28 We discuss these main components in the following sections.
Stakeholders Stakeholders are the persons and organizations who contribute to,
use, and benefit from surveillance. They typically include public health officials and staff, health-care providers, data providers and users, community representatives, government officials, and others interested in the health condition under surveillance. Stakeholders should be identified not only because they contribute to or use surveillance results, but also because they might be interested in, and can contribute to the evaluation. Stakeholders should be engaged early in the evaluation process because some might have a hand in implementing recommendations that emerge from the evaluation. Evaluations conducted without early buy-in from those responsible for conducting surveillance are often viewed as unwanted criticism and interference from outsiders and are usually ignored.
Purpose, objectives, and operations The evaluation should start with a clear statement of the purpose of
surveillance, which usually facilitates prevention or control of a health-related problem. The purpose should be followed by clearly stated objectives describing how surveillance data and their surveillance, which usually facilitates prevention or control of a health-related problem. The purpose should be followed by clearly stated objectives describing how surveillance data and their
be needed to identify cases and contacts for follow-up. To characterize the purpose, objectives, and operations of surveillance, addressing the questions at the beginning of this lesson will be helpful.
Sketching a flow chart of the method of conducting surveillance is recommended. First, identify gaps in the evaluator’s knowledge of how surveillance is being conducted. Second, provide a clear visual display of the activities of and flow of data for surveillance for those not familiar with it (Figure 5.9).
Usefulness Usefulness refers to whether surveillance contributes to prevention
and control of a health-related problem. Note that usefulness can include improved understanding of the public health implications of the health problem. Usefulness is typically assessed by determining whether surveillance meets its objectives. For example, if the primary objective of surveillance is to identify individual cases of disease to facilitate timely and effective control measures, does surveillance permit timely and accurate identification, diagnosis, treatment, or other handling of contacts when appropriate?
Usefulness of surveillance is influenced greatly by its operation, including its feedback mechanism to those who need to know, and by the presence or absence of the characteristics of optimal surveillance. Qualities or characteristics described previously in this lesson and in Appendix A affect the operation and usefulness of surveillance. Evaluation of surveillance requires assessment, either qualitatively or quantitatively, of each characteristic.
Figure 5.9 Simplified Diagram of Surveillance for a Health Problem
Source: Centers for Disease Control and Prevention. Updated guidelines for evaluating public health surveillance systems: recommendations from the guidelines working group. MMWR 2001;50(No. RR-13): p. 8.
Resource requirements (personnel and other costs) In the context of surveillance evaluation, resources refers to
finances, personnel, and other direct costs needed to operate all phases of surveillance, including any collection, analysis, and dissemination of data. The following should be identified and quantified:
• Funding sources and budget; • Personnel requirements to collect, compile, edit, analyze,
interpret, or disseminate data; and • Other resources (e.g., training, travel, supplies, and computers and related equipment).
These costs are usually assessed in light of the objectives of surveillance and its usefulness and against the expected costs of possible modifications or alternatives to the way in which surveillance is conducted.
Recommendations The purpose of evaluating surveillance for a specific disease is to
draw conclusions and make recommendations about its present state and future potential. The conclusions should state whether surveillance as it is being conducted is meeting its objectives and whether it is operating efficiently. If it is not, recommendations should address what modifications should be made to do so. Recommendations must recognize that the characteristics and costs of conducting surveillance are interrelated and potentially conflicting. For example, improving sensitivity can reduce predictive value positive and increase costs. For surveillance, recommendations should be prioritized on the basis of needs and objectives. For example, for syndromic surveillance, timeliness and sensitivity are critical, but high sensitivity increases false alarms, which can drain limited public health resources. Each characteristic must be considered and balanced to ensure that the objectives of surveillance are met. (See Appendix E for an assessment of and recommendations for notifiable disease surveillance.)