Figure 1:

During specific data collection for Public Health Surveillance in rural community

PUBLIC HEALTH SURVEILLANCE

Public health and health care practitioners are concerned with a wide spectrum of health issues including infectious diseases, chronic conditions, reproductive outcomes, environmental health, and health events related to occupation, injuries, and behaviors. This array of problems requires a variety of intervention strategies for populations in addition to the need to provide clinical preventive services for individuals. Some critical examples are the provision of prophylactic measures (e.g., vaccination or post exposure rabies prophylaxis), educational services (e.g., public health messages to diverse populations or counseling and prophylaxis for contacts of persons with certain infectious diseases), inspection of food establishments, and control of infectious and noninfectious conditions.

For these activities, the rational development of health policy depends on public health information. For example, information on the age of children with vaccine-preventable diseases has been used to establish policy on appropriate ages for delivering vaccinations (Centers for Disease Control and Prevention [CDC] 1994a). Documentation of the prevalence of elevated levels of lead (a known toxicant) in blood in the US population has been used as the justification for eliminating lead from gasoline and for documenting the effects of this intervention (Annest et al. 1983), and information on the rate at which breast cancer is detected has led to new policies regarding the ages at which to recommend mammograms (Day 1991).

Public health information is understood most basically in terms of time, place, and person. Descriptive analysis of surveillance data over time shows patterns which generate hypotheses or merely reflect patterns in reporting behavior rather than underlying disease incidence. Furthermore, the approach to the prevention and control of disease and injury is often determined by circumstances unique to the place or geographic distribution of the disease or of its causative exposures or risk-associated behavior. For example, elevated blood-lead levels in children may represent exposure to lead hazards in their environment and may require both medical and environmental interventions. Distributions of some forms of cancer (e.g., melanoma of the skin) show a definite spatial distribution (Pickle et al. 1987).

Finally, the characteristics of the person or groups who develop specific diseases or who sustain specific injuries are important in understanding the disease or injury, identifying those at high risk, and targeting intervention efforts. For example, disparities in health (incidence or severity of disease) among members of different population groups highlight the need to identify cultural, economic, or social factors associated with these health problems (CDC 1993a).

Definition and Brief History

Public health surveillance (in some literature called epidemiological surveillance) is the ongoing systematic collection, analysis, and interpretation of outcome-specific health data, closely integrated with the timely dissemination of these data to those responsible for preventing and controlling disease or injury (Thacker and Brekelman 1992). Public health surveillance systems should have the capacity to collect and analyze data (Cates and Williamson 1994), disseminate data to public health programs (Langmuir 1963), and regularly evaluate the effectiveness of the use of the disseminated data (Klaucke et al. 1988). Public health information systems, on the other hand, have been defined to include a variety of data sources essential to public health and are often used for surveillance; however, historically, they lack some critical elements of surveillance systems (Thacker 1992). For example, they may not focus on specific outcomes (e.g., vital statistics), are not ongoing (e.g., a one-time or occasional survey), or are not linked directly to public health practices (e.g., insurance claims data).

DATA COLLECTION IN REMOTE AREA OF NEPAL

The history of public health surveillance can be traced back to efforts to control the bubonic plague in the 14^th century and includes and includes such key figures as von Leibnitz, Graunt, Shattuck, and Farr (Thacker 1992). Following the discoveries of infectious disease agents in the late 1800s, the first use of scientifically based surveillance concepts in public health practice was the monitoring of contacts of persons with serious communicable diseases such as plague, smallpox, typhus, and yellow fever to detect the first signs and symptoms of disease and to begin prompt isolated. For many decades, this was the function of foreign quarantine stations throughout the world.

In the late 1940s, Alexander D. Langmuir, then the chief epidemiologist of the Communicable Disease Center (now the Centers for Disease Control and Prevention [CDC]), began to broaden the concept of surveillance. Although surveillance of persons at risk for specific disease continued at quarantine stations, Langmuir and his colleagues changed the focus of attention from individuals to diseases such as malaria and smallpox. They emphasized rapid collection and analysis of data on a particular disease with quick dissemination of the findings to those who needed to know (Langmuir 1963). As latter started by Foege et al. (1976): “The reason for collecting, analyzing, and disseminating information on a disease is to consume resources if action does not follow”. Although surveillance was originally concerned with protection of the population against infectious disease (Langmuir 1963), more recently a wide variety of health events, such as childhood lead poisoning, birth defects, injuries, and behavioral risk factors, have been included in surveillance activities (Thacker and Stroup 1994).

Unless those who set policy and implementation programs have ready access to data, the use is limited to archives and academic pursuits, and the material is therefore appropriately considered health information rather than surveillance data (Terris 1992). Thus, the boundary of surveillance practice meets with-but does not extend to actual research and implementation of intervention programs (Ballard and Duncan 1994). For example, although patient identifiers are not collected for most surveillance activities, state and local health departments may need this information for effective prevention of the spread of sexually transmitted diseases (i.e., contacting the partners of infected persons to deliver treatment and prevention information). A central difference between public health work and other biomedical research is that the boundary in public health between research and non-research activities is ill-defined (Last 1996). Specially, state and local health departments use surveillance information for control and prevention of disease, and most surveillance activities are mandated (or permitted) by state statute (CDC 1990b). If persons with contagious diseases were allowed to refuse appropriate intervention, this would have an adverse effect on the health of communities (Chorba et al. 1989). At the same time, surveillance is more than the collection of reports of health events, and data collected for other purposes may enhance surveillance activities. This extension of activities can be seen in the 1957 national weekly influenza surveillance system established by CDC which used morbidity and laboratory data from state health departments, school and industrial absenteeism, morbidity data from 108 US cities, and acute respiratory illness rates from the National Health Interview Survey (Langmuir 1987).

Uses

The uses of surveillance information can be organized on the basis of three categories of timeliness: immediate, annual, and archival (Thacker and Stroup 1994) (Figure 4-2).

• Immediate detection of:
• Epidemics
• Newly emerging health problems
• Changes in health practices
• Changes in antibiotic resistance

• Annual dissemination for:
• Estimating the magnitude of the health problem, including cost
• Assessing control activities
• Setting research priorities
• Testing hypothesis
• Facilitating planning
• Monitoring risk factors
• Monitoring changes in health practices
• Documenting distribution and spread

• Archival information for:
• Describing natural history of diseases
• Facilitating epidemiologic and laboratory research
• Validating use of preliminary data
• Setting research priorities
• Documenting distribution and spread

Immediate

For detecting epidemics, a surveillance system should allow public health officials immediate access to new information (Kilbourne 1992). For example, detection of a disease related to contaminated food or biological products should immediately trigger intervention and control efforts. As soon as, say, unusual clusters of specific birth defects or geographic clusters or pedestrian injuries [Kilbourne 1992], public health officials should respond (CDC 1990a).

In hospital and health department laboratories, various infectious agents are monitored for changes in bacterial resistance to antibiotics or antigenic composition. The detection of penicillinase-producing Neisseria gonorrhea in the United States through surveillance activities has provided critical information for the proper treatment of gonorrhea (CDC 1976). The National Nosocomial Infection Surveillance System monitors the occurrence of hospital-acquired infections, including changes in antibiotic resistance. Surveillance of influenza monitors the continual changes in the influenza virus structure, information vital to vaccine formulation (Emori et al. 1991).

Annual

Timely annual data summaries would provide immediate estimates of the magnitude of a health problem, thus assisting policy-makers to modify priorities and plan intervention programs. These same data would be useful to those assessing control activities and would help researchers establish research priorities in applied epidemiology and laboratory research.

Surveillance data are used to assess control activities programs. For example, they have demonstrated the decrease in poliomyelitis rates following the introduction of both the inactivated and oral polio vaccines and the effect on motor vehicle-associated injury of broad-based community interventions such as increased legal age of driving and seat-belt laws (Loeb 1993).

The traditional use of surveillance was to quarantine persons infected with or exposed to a particular disease and to monitor isolation activities. While this measure is rarely used today, isolation and surveillance of individuals is done for patients with multidrug-resistant tuberculosis and patients suspected of having serious, imported diseases such as the hemorrhagic fevers.

Surveillance has been used to monitor health practices such as hysterectomy, cesarean delivery, mammography, and tubal sterilization (Thacker et al. 1995). In the United States, a sociological trend is shifting in the health care industry from one dominated by a large number of small offices to one characterized by a small number of large managed-care organizations with computerized patient records. For example, as of June 1995, 32% of Medicaid beneficiaries were enrolled in managed-care organizations, compared with 14% in 1994 (CDC 1995a). Data systems developed for managed-care activities will have tremendous potential for public health surveillance.

Surveillance data serve as the cornerstone of epidemiologic and public health practice. Representative and relevant health surveillance data give the necessary framework to facilitate planning and management of public programs. For example, Missouri health officials used existing chronic disease surveillance data to develop a cardiovascular disease health plan (Thacker et al. 1995). Data used were from existing sources, including mortality, data on behavioral risk factors, and data on population distribution. The resulting plan included a task force to establish priorities and monitor progress, a plan for chronic disease control, a resource directory, and training in cardiovascular disease control strategies. As discussed later in the case study section of this chapter, officials cite the appropriate use of surveillance data as the integral component in local coalition development (Brownson et al. 1992).

The health of populations may be adversely affected by time required to do special studies. Although surveillance information has limitations, it can often be used to test hypotheses. For example, the reported occurrence of lung cancer in the United States over the past 50 years has shown the impact of changes in the prevalence of smoking behaviors in women. For example, the passage of smoking legislation in the United States was shown to increase the age of initiation of smoking (United States Department of Health and Human Services 1994). Surveillance data on cancer from the Surveillance, Epidemiology, and End Results (SEER) Program of the National Cancer Institute (Gloeckler-Ries et al. 1990) has been used as the basis of etiologic studies (Tejeda et al. 1996).

Archival

Surveillance data should be retained in readily accessible archival form, not only to document the evolving health status of a population but also to help us understand the predictors of disease and injury. For example, as we better understand spatial spread of infectious diseases such as influenza or measules, more effective prevention strategies may be possible (Longini et al. 1986; Cliff et al. 1992a). Carefully maintained archival data can provide the most accurate portrayal of the natural history of a disease in a population (Thacker and Berkelman 1992), effective measurements of the long-term effects of public policies or social changes (CDC 1991), and validation of interim data (CDC 1992; Thacker 1996).

Archival surveillance data can be used at the local, and to a lesser degree national, level to develop prevention and control activities. Missouri investigators used surveillance data to provide quantitative estimates of the magnitude of heart disease and to demonstrate an epidemic in that population. As a result, policy-makers adopted a cardiovascular health plan, enhancing its disease control program (Thacker et al. 1995). Conversely, surveillance data suggested that diabetic patients using continuous subcutaneous insulin infusion pumps suffered excess mortality; an investigation triggered by these data showed that this important technology was not associated with mortality (Teutsch et al. 1984).

Figure 3: Changes in health practice through the Micro Health Project (MHP) in rural area of Nepal.