What is disease surveillance in public health?

Public health surveillance is the ongoing, systematic collection, analysis, and interpretation of data on specific health events for use in the planning, implementation and evaluation of public health programmes.

Communicable disease surveillance is the continuous monitoring of the frequency and the distribution of disease, and death, due to infections that can be transmitted from human to human or from animals, food, water or the environment to humans, and the monitoring of risk factors for those infections.

Public health surveillance also encompasses non-communicable conditions including injury, for example poisonings.

Why do we undertake surveillance?

• Estimate magnitude of the problem
• Determine geographic distribution of illness
• Portray the natural history of a disease
• Detect epidemics/define a problem
• Generate hypotheses, stimulate research
• Evaluate control measures
• Monitor changes in infectious agents
• Detect changes in health practices
• Facilitate planning

What surveillance is ESR currently responsible for?

ESR provides a range of training opportunities through the epidemiological skills development programme. The aim of this programme is to strengthen the capacity of the New Zealand public health workforce to identify, investigate and control outbreaks of infectious and aberrant diseases. More information on the programme and its courses can be found here.

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 essential 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. In developing countries, however, surveillance systems that collect useful and representative data 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)

Data and Defining the Health Problem

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.

Data and Health Programming

Once data generated from surveillance systems are compiled and analyzed, scientists can draw a picture of the health problem and begin to develop 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 was implemented 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)

Data, Public Policy, and Funding

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)

• Incidence/prevalence
• Severity (case fatality rate)
• Mortality rate
• Productivity loss
• Premature mortality (YPLL)
• Costs in medical care
• Preventability of disease

Case Study: Control of Schistosomiasis in China

Source: http://www.cdc.gov/parasites/schistosomiasis/biology.html

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:

• Surveillance and data collection in past programs were necessary for the decision to make mass drug administration and mollusk control the primary focuses of control efforts in this particular setting.
• Surveillance systems gathering data about the success of past programs were needed in order for the areas to declare Schistosomiasis “controlled” or “eradicated” at that time.
• Shortcomings in the surveillance system were primarily responsible for the eventual failure of Schistosomiasis control programs in eight of the counties of the Sichuan Province.

As illustrated here, surveillance before, during, and after any public health program is crucial for its success.

Footnotes

(2) Nsubuga, P., White, M., Thacker, S., et al. (2006). 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.

(4) Nsubuga P., White M., Thacker S., et al. (2006). 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.

(7) Thacker, S. & Lee, L. (2011). The Cornerstone of Public Health Practice: Public Health Surveillance, 1961-2011. Retrieved May 16, 2012, from Office of Surveillance, Epidemiology and Laboratory Services, CDC.

(12) Liang, S., Yang, C., Zhong, B., & Qiu, D. (2006). Re-emerging schistosomiasis in hilly and mountainous areas of Sichuan, China. Bull World Health Organ. vol.84, n.2, pp. 139-144.

(16) Liang, S., Yang, C., Zhong, B., &  Qiu, D. (2006). Re-emerging schistosomiasis in hilly and mountainous areas of Sichuan, China. Bull World Health Organ. vol.84, n.2, pp. 139-144.

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