11.1 - Prevention

Epidemiologists, medical and public health professionals use the terms 'primary prevention', 'secondary prevention', and even 'tertiary prevention'. What is the difference between primary and secondary prevention of disease? What is an example of tertiary prevention?

Primary prevention
Primary prevention prevents the onset of disease, which may be accomplished through the removal of a risk factor. For example, eating more fruits and vegetables may reduce the risk of the onset of diabetes, insulin resistance, colon cancer, or heart disease. Immunizations against diseases are another example of primary prevention.
Secondary prevention
Secondary prevention is the detection of disease among asymptomatic persons when treatment of early disease can reduce morbidity or mortality.
Tertiary prevention
Tertiary prevention is the prevention of health deterioration once the disease is present. For instance, once diagnosed with diabetes, managing insulin levels and regularly examining feet is tertiary prevention, relieving or preventing complications of the disease.

Let's try to apply these terms (you'll find that it is not as easy as it is defined)...

  Stop and Think!

What level of prevention is:

  1. Control of blood glucose among diabetics?
  2. Increasing physical activity?
  3. Increasing physical activity among diabetics?
  4. Quitting smoking?
  5. Eliminating cigarette vending machines from places frequented by adolescents?
  6. Detecting polymorphisms for a breast-cancer gene such as \(BRCA_1\)?
  1. Control of blood glucose among diabetics? Tertiary - the disease has been diagnosed; control of blood glucose is to prevent further deterioration of health
  2. Increasing physical activity? Primary - if the individual has no obesity-related disease at present
  3. Increasing physical activity among diabetics? Tertiary - increased activity within a population defined by its disease status.
  4. Quitting smoking? Could be Primary or Secondary, depending on the damage already done to the lungs at the time of quitting; even smoking 100 cigarettes has been shown to decrease lung function
  5. Eliminating cigarette vending machines from places frequented by adolescents? Pre-Primary - we are trying to prevent adolescents from smoking by removing the opportunity to even begin smoking.
  6. Detecting polymorphisms for a breast-cancer gene such as \(BRCA_1\)? Secondary - because you are detecting an increased risk of disease, not the disease itself. This is a little bit different than measuring blood glucose for diabetes or women having mammograms to detect breast cancer because both are detecting the presence of disease. \(BRCA_1\) is associated with an increased risk for developing the disease later in life; the vast majority of women with the \(BRCA_1\) mutation don't go on to develop breast cancer.

Is prevention of disease a worthwhile effort? Danaei, Ding et al. (2009) assessed the effects of 12 modifiable risk factors on mortality in the U.S. These authors estimated that tobacco smoking and high blood pressure were responsible for 467,000 and 395,000 deaths respectively, in 2005, accounting for about one in every five or six deaths among U.S. adults. Overweight obesity and physical inactivity each accounted for 1/10 deaths. If the U.S. population was filled with active nonsmokers with controlled blood pressure who were not overweight, perhaps as many as 4/10 deaths would be averted each year! These substantial numbers support the importance of epidemiological studies applied to the prevention of disease, as opposed to simply identifying causative factors.

If a large proportion of deaths is associated with preventable risk factors, should resources be allocated to eliminating these risk factors? In the face of competing demands and finite resources, what preventative measures have the greatest impact? Which services should be the focus of clinical practice improvement and national policies and programs? Masciosek et al rank 25 evidence-based clinical primary and secondary preventative services based on their relative value to the U.S. population (as of 2004 information). The measures used for the rankings were a clinically preventable burden (CPB) and cost-effectiveness (CE). CPB was defined as the disease, injury, and premature death that would be prevented if the service were delivered at recommended intervals to a U.S. birth cohort, expressed as quality-adjusted life years. CE was defined as the average net cost per QALY gained by offering the preventative service. The Partnership for Prevention lists the rankings and provides supporting evidence on the Annals of Family medicine website. Clicking on a preventative service in the rankings brings up mortality rates, incidence rates, and risk factor prevalence by sub-population when those data are available.

  Stop and Think!

Suppose you are the health director of the state of Pennsylvania and you have options of implementing free breast cancer screening versus free vaccination of children (let's say MMR - measles, mumps, rubella) - but only enough resources for one project- which will you choose? You might consider the cost of mammography versus the cost of the vaccination. Mammography is much more expensive than MMR vaccination. Vaccination is relatively simple. The vaccine is delivered to clinics, children inoculated. Disease prevented. However, it is also important to look at effectiveness in reducing preventable mortality. How would these rankings help you reach your decision?

In this first example, N = 100 is not very large compared to n, so one should not ignore the finite population adjustment!