Choosing priority strategies for risk prevention
In constructing health policies for the prevention of well-known risks, choices need to be made between different strategies. For instance, will preventing small risks in large populations avoid more adverse health outcomes than avoiding large risks in a smaller number of high-risk individuals? What priority should be given to cost-effective interventions for primary rather than secondary prevention, such as lowering blood pressure distribution by reducing dietary salt intake compared with treatment of people with high blood pressure? Should priority be given to preventing environmental and distal risks to health, such as tackling poor sanitation or inadequate nutritional intakes, rather than the more obvious proximal risks in a causal chain? What is the most appropriate and effective mix of these strategies?
In practice there is rarely an obvious and clear choice. These strategies are usually combined so as to complement each other (1). In general, however, it is more effective to give priority to:
- population-based interventions rather than those aimed at high-risk individuals;
- primary over secondary prevention;
- controlling distal rather than proximal risks to health.
Population-based interventions or high-risk individual targets?
There is a "prevention paradox" which shows that interventions can achieve large overall health gains for whole populations but might offer only small advantages to each individual. This leads to a misperception of the benefits of preventive advice and services by people who are apparently in good health(2,3). In general, population-wide interventions have the greatest potential for prevention. For instance, in reducing risks from blood pressure and cholesterol, shifting the mean of whole populations will be more cost-effective in avoiding future heart attacks and strokes than screening programmes that aim to identify and treat all those people with defined hypertension or raised cholesterol levels, as shown in Figure 6.1 (4,6). A similar approach can be used to modify behavioural risks and environmental exposures. For example, lowering the population mean for alcohol consumption will also predictably reduce the number of people suffering from alcohol abuse (7). Often both approaches are used and successfully combined in one strategy.
Distal or proximal risks to health?
Although most epidemiological research and intervention analysis has focused on the more immediate risks for major diseases, tackling distal risks to health such as education and poverty can yield fundamental and sustained improvements to future health status. Enough is known about the predominant role of distal factors on health and survival to justify vastly greater efforts to reduce poverty and improve access to education, especially for girls. There is huge potential for major health gains through sustained intersectoral action involving other ministries and agencies concerned with development.
Primary or secondary prevention?
Risk reduction through primary prevention, such as immunization, is clearly preferable as this actually lowers future exposures and hence the incidence of new disease episodes over time. For long-term health gains it is usually preferable to remove the underlying risk. The choices may well be different, however, for different risks, depending to a large extent on how common and how widely distributed is the risk and the availability and costs of effective interventions. Large gains in health can be achieved through inexpensive treatments when primary prevention has failed. Secondary prevention is based on screening exposed populations for the early onset of subclinical illnesses and then treating them. This approach can be very effective if the disease processes are reversible, valid screening tests exist, and effective treatments are available.