Journal Issue: Children with Disabilities Volume 22 Number 1 Spring 2012
Primary versus Secondary Prevention
Prevention occurs at three levels. Primary prevention seeks to keep disabilities from developing in the first place. Secondary prevention consists of methods of screening and early detection to identify problems early, before they can do too much damage (the "nip it in the bud" approach). Tertiary prevention deals with restoring health and function to people who have already developed a disability. Secondary and tertiary prevention efforts—which are the focus of clinic-based prevention—typically involve screening or treatment. Screening and treatments are beneficial for individuals who are sick, but primary prevention is essential to reduce the prevalence of disability in a population.
The medical community is currently devoting considerable attention and resources to personalized predictive medicine—the identification of genetic markers that make a particular individual susceptible to a specific illness or disability, with the ultimate goal of tailoring therapies to individual patients. These efforts have led to early identification and some promising treatments for specific conditions such as cystic fibrosis.1 Useful clinical applications have thus far been few in number, however. Overreliance on gene discovery and personalized predictive medicine may disproportionately benefit those in the best position to take advantage of the new innovations and exacerbate the already gaping socioeconomic disparities in health by draining resources away from underfunded population-level interventions that benefit everyone (see also the article by Paul Wise in this volume).2
Moreover, the causes of many disabilities in childhood are complex and result from the interplay of environmental risk factors and genetic susceptibility; purely genetic or purely environmental disabilities exist but are rare.3 For the most common childhood conditions, primary prevention may best be achieved through universal and nonmedical interventions. As Geoffrey Rose, a pioneer in the science of prevention, wrote provocatively, "If causes can be removed, susceptibility ceases to matter."4
A key example of Rose's dictum is the dramatic decline in infant and child mortality and the subsequent rise in life expectancy in the United States over the past century. One explanation for this shift, often touted to support investments in biomedical research, credits the development of vaccines, antibiotics, and other advances in medical technology. The greatest progress in reducing deaths from many infectious diseases and extending life expectancy, however, occurred decades before the discovery or introduction of effective medical treatments.5 John and Sonja McKinlay, among others, have shown that clean water, sanitation, and changes in living conditions led to the initial improvements in public health. Especially in cramped and unsanitary urban slums, which spawned epidemics of typhoid, cholera, and tuberculosis, it was social reform and environmental engineering, not medical advances, that reduced poor health and increased life expectancy. Thus, while vaccines, antibiotics, and the development of neonatal intensive care have played a significant role in the continuing decline in infant and child mortality, the overall decline has had more to do with establishing a clean water supply than with any "medical" factor.6
Notably, few of the early "sanitarians" or bacteriologists understood the exact mechanisms by which disease was transmitted. Rather, they drew conclusions after observing the patterns of disease, which gave them sufficient information to act, even in the absence of conclusive knowledge of a mechanism. Knowing the mechanism through which environmental influences cause disease can enhance prevention and public health, however, and genetic research can be helpful in this regard.7 For example, being the victim of maltreatment (or child abuse) has been shown to be a risk factor for antisocial behavior, but questions about the causal relationship persisted because the underlying mechanism was unclear.8 One study found that males who were maltreated in childhood were more likely to exhibit violent or antisocial behavior in adolescence and young adulthood. But the risk was primarily observed in men who had a particular variant of the gene coding for monoamine oxidase A (MAOA), an enzyme that breaks down neurotransmitters.9 While several studies have confirmed the role of MAOA in conferring susceptibility, there already was, of course, sufficient evidence of the adverse consequences of maltreatment to prevent it without understanding the mechanism. Similarly, while it might be desirable and useful to understand the exact way that exposure to recognized hazards such as air pollution leads to disease and disability before regulating that exposure, it is not essential.