Useful Concepts: High Risk vs. Population Health Interventions
You will be familiar with the natural history of disease and stages of prevention, but how should we intervene?
The traditional argument was that we should screen for risk factors (hypertension, high cholesterol, etc.) and aggressively treat those at high risk: primary and secondary prevention.
Sir Geoffrey Rose introduced an innovative way of thinking about prevention.
Rose argued that focusing on people at high risk would only tackle a minority of cases of disease, for there are many more people at moderately elevated risk (those with intermediate levels of the risk factor), and in total they account for more cases of disease than do the small number of people at the high end of the distribution. This can be illustrated by serum cholesterol. The first graph shows the association between serum cholesterol levels and mortality risk. The second superimposes the population distribution of cholesterol levels (the bars), and -- the crucial point -- shows the percentage of cases that occur at each level. Note that most deaths from CVD occur in the mid range of cholesterol, merely because there are so very few people at the extremely high levels of cholesterol.
Here is a similar idea using body weight and diabetes in Canada as the example:
Perhaps, then, a more effective intervention would be to try and shift the entire distribution to the left (e.g., reducing cholesterol, or body weight across the population).
Disease, Illness & Sickness
In 1973, Mervyn Susser, an epidemiologist, proposed some distinctions that remain useful. (Susser MW. Causal thinking in the health sciences. New York: Oxford University Press, 1973)
- He used ‘illness’ to refer to the subjective sense of feeling unwell. Illness does not define a specific pathology, but refers to a person’s subjective experience of it, such as discomfort, tiredness, or general malaise. This is what the patient brings to the doctor.
- Next, the way a patient reports symptoms is influenced by his or her cultural background, and Susser used the term ‘sickness’ to refer to socially and culturally held conceptions of health conditions (e.g., the dread of cancer or the stigma of mental illness); these in turn influence how the patient reacts. Cultural conventions likewise affect where the boundary between disease and non-disease is placed: menopause may be considered a health issue in North America, but symptoms are far less commonly reported in Japan. (Melby MK, Lock M, Kaufert P. Culture and symptom reporting at menopause. Hum Reprod Update 2005; 11(5): 495-512)
- ‘Disease’ implies a focus on pathological processes that may or may not have symptoms. Where there are symptoms, these result in a patient’s illness.
- For example, a patient complains of tiredness and malaise–his illness as he experiences it. He consults a doctor about it–because he believes that he might have a sickness. The doctor might attribute the patient’s symptoms to a thyroid condition–a disease.
Link to diagram that illustrates the differences
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