The World Health Organization (WHO) defines public health surveillance as the “continuous, systematic collection, analysis and interpretation of health-related data needed for the planning, implementation, and evaluation of public health practice”.(1) The aggregation of quality health-related data is paramount to the success of all public health initiatives. Without correct and current data, diseases are misunderstood, health programs do not accomplish their goals, and resources are incorrectly allocated. Functioning surveillance systems are necessary for the success of global health initiatives. However, surveillance systems that collect useful and representative data in developing countries are often non-existent and hard to create. The failure of surveillance systems in developing countries is often due to limited available resources, lack of knowledgeable staff, disorganization, and poor infrastructure for finding and reporting cases.(2) Stronger public health surveillance systems in developing countries will allow public health officials to more accurately describe and assess the state of health problems. Reliable data can improve health promotion programs, and help policy makers and investors allocate resources effectively.(3)
A health problem must be well defined before it can be solved. Surveillance systems generate data that help public health officials understand existing and emerging infectious and non-infectious diseases. Without a proper understanding of the health problem (etiology, distribution, and mechanism of infection), it will be difficult to ameliorate the health issue. Continued data collection is needed to monitor new diseases that threaten global health security (like the Ebola virus) and the changes in distribution and virulence of well-known diseases (like the Influenza virus). Information collected on novel diseases include characteristics such as the type of pathogen involved, symptoms caused, the infected population, and the morbidity and mortality rates.(4) Without surveillance, public health officials would be stabbing blindly at health problems, which is a waste of precious resources. Understanding the pathogen involved helps scientists understand where and how to intervene.
Once data generated from surveillance systems are compiled and analyzed, scientists can draw a picture of the health problem, and begin to create public health interventions. Evidence-based practice in public health depends on current and correct data.(5) After a program is created and implemented, continued surveillance is important to the program’s evaluation. Program evaluation allows leaders to modify the program to make it more successful.(6)
The Smallpox Eradication Program (1966 to 1978) eradicated the smallpox virus through education and mass vaccination programs across the globe. A competent and integrated surveillance system was crucial to the success of the program. As new cases were reported, ring vaccination occurred to prevent the spread of the illness to non-immunized people.(7) Without a network that allowed for quick detection and action, smallpox might never have been eradicated. Surveillance is vital in control, elimination, and eradication initiatives, but it is often where programs fail. Governments and organizations should understand the importance of surveillance in disease and epidemic control, because in many cases, when surveillance fails, the program fails, as demonstrated in a case study below.(8)
Surveillance systems that generate specific data on diseases and geographic areas are imperative because they help measure the relative importance of a health event.(9) Facts about disease distribution and determinants that come from surveillance help politicians and organizations make more informed decisions about where, when, and how to spend money and time in order to elicit the best results. Without quality public health data, interventions may be misguided and wasteful.(10) Numbers and statistics should be the basis upon which funders and politicians make their decisions. Confidence in the surveillance system that generated these numbers is crucial in resource allocation. Should more money go towards controlling a disease that kills one million people per year, or one thousand? Such questions cannot even be raised without surveillance and data collection.
The main types of information collected by surveillance systems to measure the relative importance of a disease are:(11)
The re-emergence of Schistosomiasis in the Sichuan province of China is a perfect example of the importance of ongoing surveillance and data collection before, during, and after the implementation of a disease control program.(12) Schistosomiasis is caused by a parasitic worm infection. A person contracts Schistosomiasis after he or she is exposed to water that contains the Schistosoma parasites, which enter the body through the skin. The life cycle of a Schistosoma worm is complex and includes a stage in which the parasite matures in a specific type of freshwater snail.(13) More than 200 million people worldwide contract this type of parasitic worm infection.(14) Without treatment, the disease can progress into a chronic state, producing symptoms such as stomach pain, liver enlargement, fever, chills, and an increased risk of bladder cancer.(15)
Over the past few decades, the Sichuan province has been very successful in its efforts to control Schistosomiasis. The program to stop transmission of the disease included mass drug campaigns and the use of pesticides to kill the snail hosts implicated in the life cycle of the parasites.(16) These programs were widely successful. However a follow-up study showed that there were eight counties (that had previously declared themselves as having controlled the disease) where the disease was reemerging.(17) Clearly, control efforts had failed at some step in the system.
Those who conducted the study (including two scientists from the CDC in China and one from the School of Public Health at UC-Berkeley), believed that the failure of the public health initiative to keep Schistosomiasis under control in parts of the Sichuan province was largely due to the failure of the program’s surveillance system. The surveillance system was not continuing to coordinate effectively with all parties involved; it was not closely monitoring the snail population in the area, nor was it seeking potential new Schistosomiasis cases.(18) The study concluded that the “early implementation of an optimal surveillance system should be made a public health priority”.(19)
This case study demonstrates the importance of surveillance systems and data collection in multiple ways:
As illustrated here, surveillance before, during, and after any public health program is crucial for its success.
(1)Public Health Surveillance. (2012). Retrieved May 16, 2012, from World Health Organization.
(2) Nsubuga P, White ME, Thacker SB, et al. Public Health Surveillance: A Tool for Targeting and Monitoring Interventions. In: Jamison DT, Breman JG, Measham AR, et al., editors. Disease Control Priorities in Developing Countries. 2nd edition. Washington (DC): World Bank; 2006.
(3) Heymann, D. L. (2006, February). Control, elimination, eradication and the re-emergence of infectious diseases: getting the message right. Retrieved from Bulletin of the World Health Organization.
(4) Nsubuga P, White ME, Thacker SB, et al. Public Health Surveillance: A Tool for Targeting and Monitoring Interventions. In: Jamison DT, Breman JG, Measham AR, et al., editors. Disease Control Priorities in Developing Countries. 2nd edition. Washington (DC): World Bank; 2006.
(7) Thacker, S. B., MD., & Lee, L. M., PhD. (2011, October 7). The Cornerstone of Public Health Practice: Public Health Surveillance, 1961-2011. Retrieved May 16, 2012, from Office of Surveillance, Epidemiology and Laboratory Services, CDC.
(8) Heymann, D. L. (2006, February). Control, elimination, eradication and the re-emergence of infectious diseases: getting the message right. Retrieved from Bulletin of the World Health Organization.
(9) Klaucke, D. N., M.D., Buehler, J. W., M.D., Thacker, S. B., M.D., Parrish, R. G., M.D., Trowbridge, F. L., M.D., & Berkelman, R. L., M.D. (1988, May 6). Guidelines for Evaluating Surveillance Systems. Retrieved May 17, 2012, from Centers for Disease Control and Prevention.
(12) Liang, Song; Yang, Changhong; Zhong, Bo and Qiu, Dongchuan. Re-emerging schistosomiasis in hilly and mountainous areas of Sichuan, China. Bull World Health Organ [online]. 2006, vol.84, n.2 [cited 2012-05-29], pp. 139-144.
(13)Schistosomiasis Biology. (2010, November 2). Retrieved May 22, 2012, from Centers for Disease Control and Prevention.
(14)Schistosomiasis. (2010, November 2). Retrieved May 22, 2012, from Centers for Disease Control and Prevention.
(15)Schistosomiasis Disease. (2010, November 2). Retrieved May 22, 2012, from Centers for Disease Control and Prevention.
(16) Liang, Song; Yang, Changhong; Zhong, Bo and Qiu, Dongchuan. Re-emerging schistosomiasis in hilly and mountainous areas of Sichuan, China. Bull World Health Organ [online]. 2006, vol.84, n.2 [cited 2012-05-29], pp. 139-144.