Chapter 2: Epidemiology

INTRODUCTION

Injury is not an “accident” but rather a disease, much like malaria, tuberculosis and other public health problems, or cancer and heart disease. Injury, like other diseases, has variants such as blunt or penetrating. It has degrees of severity, rates of incidence, prevalence, and mortality that can differ by race and other sociodemographic factors. Injuries have a predictable pattern of occurrence related to age, sex, alcohol and other drugs, and again, sociodemographic factors, among others. They also have a predictable prognosis, based on age, sociodemographic factors, as well as injury severity.

This characterization of injury as a disease is an important one, and a matter of more than just semantics. It is only when public health concepts are applied to this disease of injury that it, like other public health diseases, can be controlled to a socially acceptable level. The first step after its recognition as a disease is to characterize the disease such that control strategies can be applied. Epidemiology is the study of patterns of disease occurrence in human populations and the factors that influence these patterns.¹ Thus, the majority of injury epidemiology relates to describing specific populations and the factors that influence injury occurrence in these populations.

Descriptive epidemiology refers to the distribution of disease over time, place, and within or across specific subgroups of the population. It is important for understanding the impact of injury in a population and identifying opportunities for intervention. The burden of injury can be described as the most common, most fatal, most debilitating, or most costly within a specific population.

Analytic epidemiology, in contrast, refers to the more detailed study of the determinants of observed distributions of disease in terms of causal factors. The epidemiological framework traditionally identifies these factors as related to the host (ie, characteristics intrinsic to the person), the agent (physical, chemical, nutritive, or infectious), and the environment (ie, characteristics extrinsic to the individual that influence exposure or susceptibility to the agent). The environment can be physical or sociocultural. The importance of this epidemiological approach is the direction it gives to injury prevention efforts as well as directing areas requiring further research.

Injuries can result from acute exposure to physical agents such as mechanical energy, heat, electricity, chemicals, and ionizing radiation in amounts or rates above or below the threshold of human tolerance.² The transfer of mechanical energy accounts for more than three quarters of all injuries.³ The extent and severity of injury is largely determined by the amount of energy outside the threshold of human tolerance. Both the exposure to energy and the consequences of that exposure are greatly influenced by a variety of factors both within and beyond individual or societal control.⁴

The concepts of the public health approach applied to injury control seek to modulate factors related to the host and agent and/or their interactions within the environment ...