Surveillance Systems: Two Quantitative Methods

¶ … surveillance systems: Two quantitative methods for evaluation of a surveillance system and two qualitative methods for evaluation of a surveillance system.

Quantitative assessments of surveillance systems revolve around two key numerical measures: sensitivity and specificity. Sensitivity, expressed as a percentage between 0 and 100, calculates the proportion of all actual manifestations of the disease that are detected by the surveillance system. It is the degree to which the surveillance system can 'pick up' or detect cases of the disease. Specificity, also expressed as a percentage between 0 and 100, is the opposite of sensitivity. It the proportion of all persons without the disease accurately detected by the system. Specificity is often more difficult to calculate than sensitivity and more expensive to keep track of, in many instances, thus it is less frequently used.

Qualitative methods of evaluating a system include a system's flexibility, or the ability to adapt to a change in the environment. This might include a new possible health outcome or risk factor. For example, when tracking the spread of swine flu, increased rates of school absenteeism might need to be added to a system, after the end of summer vacation. A second qualitative measure is acceptability or to the degree that the healthcare providers, hospitals, and laboratories who will be accumulating and evaluating the data perceive the surveillance system to be as acceptable. Is the system relevant? Can the methods required by the system fit in with the needs of an average workday? Is it ethical? It also must be easy to use and minimally time-consuming. Simplicity is another qualitative measure, related to acceptability, referring to a surveillance system's ease of use. Data must not only be simple to record, but simple to understand, once it is tabulated, so it can be useful.

Q2: Other Surveillance System: Existing surveillance system not described in the lesson

Data sources: The nature of the British nationalized healthcare system (NHS) is that every citizen must register with a GP (general practitioner). Then, the patient can receive free care or referrals to specialists from the doctor. GPs thus can provide comprehensive data regarding patients with a variety of conditions, from a wide range of demographic groups. Currently, 3,500 GP practices, encompassing a population of 23 million patients, contribute to the national QSurveillance database. The system is the largest and most regularly updated health tracking system in the world (National disease surveillance, 2009, BJCIM).

The system can respond effectively to health alerts. For example, given concerns over the swine flu epidemic upon the horizon, "the QSurveillance primary care tracking database has increased the level of detail" in its regular weekly and daily reports to government and health authorities. Daily reporting now includes: "patients reporting flu-like symptoms in the last day, patients with flu who have been prescribed antivirals, patients prescribed antivirals without a confirmed flu diagnosis, hospital admissions related to flu, the uptake of flu vaccinations, and the uptake of childhood immunizations and patients reporting severe asthma or vomiting and diarrhea that could be flu" and confirmed flu-related deaths (National disease surveillance, 2009, BJCIM).