Epidemiological basis for preventive strategies

Approaches to prevention

Prevention can be considered on a number of levels:

Primordial prevention - seeks to prevent at a very early stage, often before the risk factor is present in the particular context, the activities which encourage the emergence of lifestyles, behaviours and exposure patterns that contribute to increased risk of disease. For example, a child seeing their parents smoke cigarettes may wrongly consider this a good lifestyle choice for later in life: advising parents to quit smoking in such circumstances can be considered primordial prevention.

Primary prevention - prevention of disease through the control of exposure to risk factors. Strategies for primary prevention include population-wide strategies and targeted, high-risk strategies focusing on population sub-groups. For example, careful weight control prevents obesity which in itself is a risk factor for many conditions including heart disease and diabetes.

Secondary prevention - the application of available measures to detect early departures from health and to introduce appropriate treatment and interventions. Screening is a major component of secondary prevention for example, cervical screening for women to detect early changes which may go on to lead to cancer of the cervix.

Tertiary prevention - the application of measures to reduce or eliminate long-term impairments and disabilities, minimising suffering caused by existing departures from good health and to promote the patient’s adjustments to his/her condition. For example, a person identified as having type 2 diabetes will have regular blood glucose checks to monitor control of their diabetes and prevent complications of the disease.

Targeting populations versus high-risk only groups

There are two approaches to prevention - targeting a whole population whether they are exposed to risk factors or not, or tackling only those identified as being high risk. There are pros and cons to each approach.

The prevention paradox: aka the Rose hypothesis (1992)^[25]
Since diseases are rare, most individuals who adopt a behaviour designed to lower their risk of disease will not benefit directly, although a few individuals may benefit enormously. For example, any one person’s decision to lose weight may only have a small impact on that person’s risk of disease in the near future, but if many people each lose a little weight, this may have a substantial impact on the community’s obesity-related disorders.

Although individuals with high risk factors may benefit from interventions specifically targeted at them, the effect on the overall incidence of the disease will be limited in the absence of a population-oriented intervention.

High risk approach

Population approach

Advantages

May be more cost-effective than population wide approaches
Those who are identified as being high risk may be more motivated to change their behaviour than the whole of society
Easier for health professionals to promote change on an individual basis
Individuals are usually aware of their exposure to adverse risk, whereas in society not everyone will have been exposed
Society prefers focusing on individuals to change rather than a whole population

Recognises that society influences individual behaviour
Risk reduction can be achieved at population rather than individual level
In situations where there is a dose-response relationship in terms of risk and exposure, shifting the entire population distribution towards lower levels of exposure is effective.

Disadvantages

Can be expensive to identify and treat those at increased risk
Fails to address public health problems arising from small but widespread risks that may be substantial
Ignores the point that a large number of people exposed to a small risk may generate more cases than a small number of people exposed to a large risk
Tends to medicalise prevention
Strategies for the individual tend to be either palliative or temporary
Does not focus on what influences behaviour
Does not tend to predict an individual’s change in risk
May have little overall impact on control of disease

Is less effective in situations where there is not a dose-response relationship in terms of risk and exposure.

Whilst the high-risk approach seemingly has many more disadvantages compared to the population approach, the prevention paradox reduces the effectiveness of the population approach, therefore a combination of population and high-risk approaches is usually most effective.

High risk groups can be identified through screening, genetic testing, analytical studies linking risk factors and disease and ecological studies to identify groups.^[26]

References

[25] Rose G (1992). The strategy of preventive medicine. Oxford University Press, Oxford.
[26] Lewis et al. Mastering Public Health. A postgraduate guide to examinations and revalidation. Royal Society of Medicine press. 2014