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Disease prevention: helping health professionals

A new controversy about “how to stay well” hits the media at least once a week. Recent examples include: disease prevention claims made for various “healthy foods;” proposed policies to tackle the obesity pandemic, such as sugar or soda taxes; the benefits versus risks of long-term statins in healthy persons; the value of prostate cancer screening; and the accuracy of new genetic tests to predict future disease. In all these debates, the bottom line is much the same: the controversy is scientifically complicated, and senior medical experts take both sides — leaving the average health professional and patient confused.

Notably, the controversies which affect the largest number of persons, who are clinically well – including all the examples above – are about prevention: undergoing some medical or lifestyle intervention now, for promised health benefits later, in the long run. Scientific methods of analysis of the pros and cons of such preventive interventions are well developed but poorly understood by most practising health professionals, in both the clinical and public health communities.

Particularly badly taught in most health professional training is the principle that all preventive measures have the potential to do more harm than good. Preventive measures, virtually never “cost-free,” also have the potential to be a non-competitive use of scarce healthcare, public health, or personal resources. An important ethical issue thus presents itself: how does one rein in the promotion of scientifically unsupported preventive measures for well individuals, and for entire healthy populations? One thing is certain: this dubious practice is remarkably common in the annals of recent medical and public health history. That does not have to be the case.

By the original uploader Rsabbatini at English Wikipedia. CC BY 4.0 via Wikimedia Commons
Dr. John Snow (1813-1858), British physician. Image by Rsabbatini at English Wikipedia. CC BY 4.0 via Wikimedia Commons.

The basic science with the best credentials for evaluating the worth of disease prevention is epidemiology – the quantitative study of who becomes ill (or dies), who does not, why, and what can be done about it. Over a century ago, two of epidemiology’s most famous early investigators, John Snow and Joseph Goldberger, developed statistical methods for investigating the causes of two lethal epidemic diseases for which the cause was then unknown: cholera (in London) and pellagra (in the American South). The Snow and Goldberger stories still shed light on how modern epidemiologists assess a body of scientific studies to know whether a particular exposure credibly causes a given disease. (Exposure here can mean environmental hazards; potentially harmful or beneficial diets; aspects of lifestyle such as physical activity; or use of a recreational substance such as tobacco, alcohol, or illicit drugs.) These pioneers began the process of providing us with the epidemiological tools we have today for analysing modern scientific evidence about the pros and cons of proposed new preventive treatments or policies.

The core tool kit for such analyses is a distinct sub-set of Critical Appraisal checklists developed by epidemiologists over the last few decades to assess scientific studies’ quality. The epidemiological categories of scientific study most relevant to assessing any preventive intervention are:

  • Causation
  • Efficacy and effectiveness
  • Health economic (e.g. cost-effectiveness) appraisals
  • Systematic reviews/meta-analyses
  • Health inequalities impact assessments

These analytic tools, had they been robustly applied to preventive medical interventions that later turned out to have “done more harm than good,” might well have prevented major recent episodes of iatrogenic (doctor-caused) disease. Examples (many rejected only after widespread but premature use led to clear-cut health problems) include: routine hormone replacement therapy for menopausal women; an early rotavirus vaccine that occasionally caused intussusception, an acute surgical emergency in infants; prostate cancer screening with the PSA blood test; and oral beta-carotene (a Vitamin A pre-cursor) for cancer prevention — all within the last 30 years.

Preventive measures, virtually never “cost-free,” also have the potential to be a non-competitive use of scarce healthcare, public health or personal resources.

Claims made in recent years for the benefits of newly developed, but not yet thoroughly evaluated, medical preventive interventions have thankfully become more contentious. Witness the ongoing controversy around what sorts of evidence are scientifically required to justify lifelong daily statin treatment for a third of healthy US middle-aged and elderly adults, as recommended by American College of Cardiology/American Heart Association national guidelines in 2013 (or about 25% of that population in the UK, according to more conservative 2014 NICE Guidelines). Future generations of health professionals will need strong critical appraisal skills in order to sort out sound versus bogus interpretations of the complex science behind such controversies — thereby defending, as professional ethics require, their patients and local communities from potentially harmful or resource-inefficient prevention proposals.

Our experience is that every health professional is capable of mastering these analytic techniques, which are increasingly being included in undergraduate training worldwide. We call on those responsible for both basic and continuing health professional training to increase the content, in those educational programmes, of critical appraisal skills for evaluating prevention specifically. We are not suggesting that critical appraisal skills for the rest of clinical practice — diagnosis, prognostication, and assessing treatment effectiveness and efficiency — are not important. However, we humbly submit that the average practitioner has the potential to harm many more persons — and waste many more resources — with widely recommended, but scientifically unjustified, preventive interventions, compared to treatments for active disease. This is simply because preventive guidelines tend to apply, for many years at a time, to the much larger number of well persons in the general population, compared to the rather small number of patients who are acutely ill at any one time.

To conclude, knowing how to tell useful from harmful or wasteful prevention is a core competency for both clinical and public health professionals; more should be done to ensure that they all acquire that competency.

Featured image credit: Photo by Jesse Oricho. CC0 public domain via Unsplash.

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