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INTRODUCTION

In this chapter, we review the epidemiologic concepts underlying the prevention and control of infectious diseases. While public health and medical professionals are familiar with the interventions commonly used to prevent or control infectious diseases, the underlying epidemiologic concepts that drive and guide these interventions may be less familiar. Although we focus on acute infectious diseases, these concepts are broadly applicable to communicable diseases, including chronic or neoplastic diseases caused by exogenous transmissible agents such as human immunodeficiency virus (HIV), hepatitis B and C viruses (HBV and HCV), human papilloma virus, and prions.

A better understanding of the core epidemiologic concepts can: (1) help researchers prioritize, design, and conduct studies to identify and optimize prevention and control interventions; (2) assist clinicians in understanding their role and how it directly and indirectly contributes to containment efforts; (3) aid field investigators in developing and using a systematic and comprehensive approach to hypothesis generation and testing when conducting outbreak investigations; (4) help responders design, implement, and evaluate interventions to control and prevent acute microbial threats (Box 82-1), as well as endemic infectious diseases; and (5) facilitate the design, testing, and evaluation of infectious disease emergency operations response plans by policy makers and planners.

BOX 82-1 Common Interventions to Prevent and Control Infectious Diseases

Control Measures

Alt er risk factors

Prophylactic immunization

Postexposure management

Diagnosis and treatment

Infection control practices

Case finding and isolation

Contact tracing and quarantine

Environmental control measures

Identify and control infectious sources

Our primary focus is on infectious disease transmission mechanisms, transmission dynamics, and transmission containment. The design, implementation, and evaluation of strategies to control infectious diseases can be improved by using a systematic, integrated epidemiologic approach, especially for acute or novel microbial threats that require special public health actions (e.g., severe acute respiratory syndrome (SARS), human pandemic influenza, or bioterrorism). Furthermore, we stress the value and importance of understanding the epidemiologic control points that drive infectious disease transmission dynamics.

EPIDEMIOLOGIC CONCEPTS

Epidemiology is “[t]he study of the distribution and determinants of health related states and events in populations, and the application of this study to control health problems.”1 By health-related states or events, we mean the occurrence or condition of infection, disease, injury, disability, or death. Epidemiologic studies are designed to answer well-defined investigative questions while minimizing threats to valid inference (e.g., random and systematic error). Most medical and public health professionals are familiar with the epidemiologic approach to public health action. Infectious diseases differ in important ways from noninfectious diseases because of the mechanisms by which microbial agents are transmitted and the population dynamics of transmission and disease occurrence. To improve our conceptual understanding, we use a systematic, comprehensive, and integrated approach (Fig. 82-1). Specifically, we cover the following:

  1. Transmission mechanisms

    1. Chain model of infectious diseases;

    2. Natural history of infection and infectiousness; and

    3. Convergence ...

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