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Building a Community Health Surveillance System
by Bill Davenhall
Esri Health and Human Services Solutions Manager

Editor's note: A community health surveillance system (CHSS) is a network that constantly gathers, integrates, and analyzes data on indicators, occurrences, and transmissions of disease; monitors the capabilities of the health system; and spatially relates all this information using GIS. This proactive approach deals more effectively with health threats, particularly those caused by the use of bioweapons.

CHSS data includes clinical data, such as symptoms and diagnostic results, and geographic information such as the locations of patients, medical assets, and outbreaks.

Geography plays a major role in understanding the dynamics of health and the spread of disease. Often referred to as disease tracking or outbreak analysis, the methodologies used in determining the causes and predicting the impact of a disease outbreak are based on a thorough analysis of the geography of disease. Recent cases of anthrax and the fear of biological warfare have increased concerns about the ability of the public health system to handle a major disease outbreak.

Tara O'Toole, a physician, public health professional, and deputy director of the Johns Hopkins University Center for Civilian Biodefense Studies, testified before the United States Congress on July 23, 2001, regarding the country's ability to respond to bioterrorist events. "A covert bioterrist attack would likely come to attention gradually, as physicians became aware of an accumulation of inexplicable deaths among previously healthy people. The speed and accuracy with which doctors and laboratories reached correct diagnoses and reported their findings to public health authorities would directly affect the number of deaths."

Dr. O'Toole also testified that the health care system is "operationally fragile and inelastic" and lacks the surge capacity to handle a sudden influx of critically ill patients. "Moreover, systems that are used only in rare emergencies seldom work as planned," she added. In the absence of any continuous and comprehensive health monitoring system, most experts agree that the public health community won't have much advanced warning of such an attack.

It is not always immediately obvious that a lethal infectious agent is present. Most public health epidemiological tools are used only after an actual or suspected outbreak is reported. Typically, by the time a disease outbreak is brought to the attention of epidemiologists, the infected individual has interacted with the immediate population and exposure to the disease has already taken place.

While the work of epidemiologists is rigorous and clinically sound, it is limited in scope, geographically speaking. Outbreaks of anthrax or smallpox in more than one community simultaneously, even in the United States, could overburden the agencies that diagnose and report outbreaks. CHSS, a proactive and geographically based approach, provides early warning of disease outbreaks.

What Is CHSS?

A health surveillance system continually measures the level of health protection as well as the occurrence of disease in a population. It requires a lower threshold for action than disease surveillance. By the time someone is admitted to an acute care hospital with a communicable disease, that person may have been symptomatic for days or weeks and may have already been seen by health care professionals repeatedly.

For example, smallpox, which begins with a rash that becomes more painful and extensive, is often initially treated with an anti-inflammatory drug such as Benadryl [brand name for the antihistamine Diphenhydramine HCL]. When this treatment proves ineffective, lab work is ordered and the diagnosis made. From a community health perspective, a spike in the number of prescriptions for Benadryl in one area could be used as an indicator of a possible smallpox outbreak.

GIS is a powerful tool for responding to disease outbreaks and has become a staple tool of epidemiological investigators. CHSS should incorporate a GIS-based incident tracking system. However the transition from episodic investigation to ongoing monitoring using GIS requires more robust data collection and analysis. CHSS relies on a continuous stream of clinical data that is gathered automatically across geopolitical boundaries.

Human intervention should not be required until preestablished panic levels-in the number and/or clustering of occurrences-are reached. This rules-based system uses data interpretations made by epidemiologists and other public health officials. Air quality systems found in most urban areas of the country provide a good example of this type of system. These systems monitor continuously and automatically report air contaminates to a centralized analysis system. The system reacts only when critical levels, established by experts, have been reached.

The Role of Public Health Agencies

Traditionally, public health agencies have played a behind-the-scenes role. Although these agencies have vast powers that can be exercised when the public is clearly at risk, most of the time they work tirelessly, in relative obscurity, protecting the public. The public health system has been fine-tuned to respond to extreme, but fairly limited, disease outbreaks.

However, this system lacks the resources for maintaining a state of readiness for an extended period of time. In addition to concerns about the scope and duration of response to natural disease outbreaks, public health experts believe that a different response is needed for bioterrorist-caused disease outbreaks.

For CHSS to succeed, public health officials at the local, state, and federal levels must provide leadership. This leadership includes setting clearly articulated standards for technology, data access and use, and the training necessary to create and maintain the system. Public health agencies must promote participation agreements that implement clinical information exchanges and secure anonymity for patients.

Capturing Data for CHSS

CHSS data includes clinical data, such as symptoms and diagnostic results, and geographic information such as the locations of patients, medical assets, and outbreaks. Population-based data must also describe relatively small geographical areas such as ZIP Codes, city blocks, census block groups, or point locations. Data that reflects the level of "wellness" of a population in a geographic area is necessary to draw inferences about changes in health levels and exposure to disease.

According to 1999 statistics from the Centers for Disease Control and Prevention (CDC), on any given day, approximately 2.1 million people go to see the doctor in the United States. An initial diagnosis is usually followed by diagnostic tests and a final diagnosis. Both diagnoses, initial and final, are typically in digital form and available to a health information system by day's end. Some health care providers are using handheld technology that transmits this information immediately.

This data, already in a format that can be integrated into a CHSS, can also be further enhanced with the use of an international classification system (ICD9-10). ICD9-10 assigns standard codes to all diseases, diagnostic procedures, and surgical procedures. This reduces data errors and allows seamless analysis of disease across geopolitical borders.

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