Module Components

• Overview

Topics

• Definitions
• Epidemiologic Frameworks
• Communicable and Emerging Infectious Diseases
• Role of the Public Health Nurse

Nurs 467 - Public Health Nursing

Module 4: Epidemiology, Communicable Disease and Emerging Infectious Diseases

DEFINITIONS

Attack Rate – the number of people exposed to a particular agent and became ill divided by the total number of people exposed (similar to incidence but time frame is confined to a short period around a specific exposure – think of food-borne outbreaks).

Bioterrorism - the deliberate release of viruses, bacteria, or other germs (agents) used to cause illness or death in people, animals, or plants. These agents are typically found in nature, but it is possible that they could be changed to increase their ability to cause disease, make them resistant to current medicines, or to increase their ability to be spread into the environment (CDC).

Endemic – population has an expected level of the disease that isn’t necessarily higher than normal; for example, hepatitis B is endemic in parts of the world

Epidemic – more cases of a particular disease than expected in a given area or among a specific group of people, over a particular period of time; also called “outbreak”

Epidemiology – the discipline that provides the structure for systematically studying the distribution and determinants of health, disease and conditions related to health status. 

Incidence – The rate at which a specific disease develops in a population (a measure of risk). The incidence rate is the number of new cases of an illness or injury that occurs within a specified time.  Incidence is a measure of risk.  The denominator includes everyone at risk for developing the disease and the numerator includes all of the new cases. You must have a defined time period for incidence (i.e. all new cases in the past 6 months).

Infant Mortality Rate - (IMR) is the number of infant deaths (deaths that occur in the first year of life) divided by the total number of live births for the specified time period (usually one year). IMRs are used around the world as an indicator of overall population health and availability of health services.

Morbidity rates – the rate of disease or the rate of sickness, can be shown through incidence (new occurrences) or prevalence (all cases at that timepoint).

Mortality rates – the rate of death, these are key epidemiologic indicators but informative only for fatal diseases and do not provide direct information about either the level of existing disease in the population or the risk of getting any particular disease. Mortality rates are actually proportions.

Pandemic – epidemic that occurs worldwide or over a very wide area, crossing international boundaries and usually affecting large numbers of people

Proportion– a type of ratio that tells us what fraction of a population is affected. The numerator is the number of people affected and the denominator is the total population. For example, if in 2002 there were 2,000,000 million deaths in the US of which there are 500,000 caused by heart disease.  The proportion of deaths caused by heart disease is 500,000/2,000,000 = .25 or 25%.

Prevalence – prevalence is the proportion of people in a population who have a particular disease at a specified point in time.  Prevalence includes all of the new cases (incidence) and all of the existing cases. Prevalence is a snapshot of a disease at a single point in time; it doesn’t give any information on how many cases are new versus old.

Rate - a statistic used to describe an event or characteristic over time.  In epidemiology a rate is used to make comparisons among populations or to compare a subgroup of the population (specific rate) with the total population.  Rates are used to help us understand how fast a disease is occurring in a population.

Ratio – a statistic used to compare one number with another. A ratio is often used to compare one population with another (i.e. people with heart disease in City A versus people with heart disease in City B).

Risk - refers to the probability that something will occur within a specific time.