NR 442 Week 2 Epidemiology & Communicable Disease

NR 442 Week 2 Epidemiology & Communicable Disease

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Chamberlain University

NR-442 Community Health Nursing

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Date

Week 2 Epidemiology

Foundations of Epidemiology

Epidemiology refers to the study of how health-related events, including diseases, are distributed within populations and what factors influence or determine this distribution. This field seeks to understand patterns of disease occurrence by focusing on the person, place, and time—commonly referred to as the Person-Place-Time Model. This model addresses questions such as who is affected, where cases are found, and when they occur.

The agent in epidemiology signifies the cause of the disease, while the host encompasses the individual exposed to the agent and their response, which can be influenced by various intrinsic factors. The environment includes extrinsic elements that enable the transmission or development of disease.

Key Determinants in Disease Development

The table below outlines the main components of the epidemiologic triad:

Nutritive elements may involve both excessive intake and deficiencies. Chemical agents such as toxins or allergens, physical agents like radiation or mechanical forces, and infectious agents (including viruses, bacteria, fungi, protozoa, and metazoa) all contribute to disease emergence.

Host susceptibility can vary due to age, sex, inherited traits, immune status (active or passive immunity), coexisting health conditions, and personal behaviors that impact exposure risk or vulnerability.

Epidemiological Models and Measures

The epidemiological triangle model simplifies the understanding of disease interaction through the interplay of agent, host, and environment. A more holistic approach, the ecosocial perspective, integrates broader social and environmental influences—such as poverty, discrimination, and policy—along with microbiological factors.

Rates and Ratios in Epidemiology Epidemiologists use various calculations to interpret disease frequency and distribution. For example, if 15 out of 500 students tested positive for tuberculosis, this gives a rate of 15/500 = 0.03, or 30 per 1,000 students.

Key epidemiological metrics include:

• Incidence: The count of new cases over a specific period.
• Prevalence: The total number of existing cases at a given time.
• Crude rates: Summarize general data like birth or death rates without accounting for specific demographics.
• Proportionate Mortality Ratio (PMR): The percentage of total deaths attributed to a specific cause.

Six fundamental criteria often support the inference of a cause-and-effect relationship in public health investigations:

1. Strength of association
2. Dose-response relationship
3. Temporal sequence
4. Biological plausibility
5. Consistency across studies
6. Specificity of association

Chapter 26: Communicable Disease

Disease Progression and Periods

Communicable diseases progress through distinct phases. The latent period marks the stage after the agent enters the host but before the host becomes infectious. During this phase, replication begins but no shedding occurs. The communicable period follows, starting with the shedding of the infectious agent. The incubation period spans from the point of infection to the appearance of clinical symptoms. Notably, the incubation phase may coincide with the communicable period, meaning individuals can spread the disease before showing symptoms.

Chain of Infection

The transmission of communicable diseases typically follows a six-link chain:

Immunity and Vaccination

Immunity is classified as either natural or acquired. Natural immunity can be active—developed through prior infection—or passive, such as antibodies passed from mother to child. Acquired immunity arises through medical intervention. Active acquired immunity develops following vaccination, while passive acquired immunity involves externally supplied antibodies like monoclonal antibodies or blood products.

Vaccine failure can occur in two ways:

• Primary vaccine failure: No immune response post-vaccination.
• Secondary vaccine failure: Loss of immunity after initial protection.

Diseases are identified based on confirmed or probable diagnosis through a combination of clinical symptoms, lab confirmation, epidemiological connection, or genetic typing.

Immunization Terms and Considerations

The term immunization broadly describes the process (either passive or active) that enhances the body’s defense against infectious diseases. In contrast, vaccination specifically refers to the administration of a vaccine or toxoid to produce active immunity.

Vaccination is generally safe; however, contraindications exist. These may include pregnancy, immunocompromised status, or even mild illness in certain situations.

References

Centers for Disease Control and Prevention. (2020). Principles of epidemiology in public health practice (3rd ed.). U.S. Department of Health and Human Services. Stanhope, M., & Lancaster, J. (2020). Public health nursing: Population-centered health care in the community (10th ed.). Elsevier. World Health Organization. (2022). Immunization, vaccines and biologicals. https://www.who.int/teams/immunization-vaccines-and-biologicals