Disease Occurrence, Distribution, and Patterns

Introduction

Do you know how we came up with the label "flu season"? We refer to the time between December and March as flu season because epidemiologists have studied the occurrence of the flu and concluded that a majority of flu cases occur during this time of the year. Lessons in this module will show you how scientists measure the occurrence of disease and track the distribution of disease while trying to analyze patterns of illness.

Essentials Questions

How do we keep track of disease occurrence and monitor the emergence of new diseases?
What are key sources of disease surveillance data?
How can analyzing patterns of illness help scientists?
How do we use epidemiological data to study disease?
How does public health surveillance data benefit society?

Key Terms

Mortality rate - the ratio of the total number of deaths to the total population.
Morbidity rate - The sickness rate, the number of people who are sick or have a disease compared with the number who are well.
Disease frequency - the number of cases that occur over a given time period.
Incidence cases - new cases during a given time period.
Prevalence cases - all cases during a given time period.
Case fatality rate - proportion of people with a disease who die from it.
Birth rate - calculated by dividing the number of live births during a specified time period by the population from which the births occurred typically expressed as the number of live births per 1,000 people.
Attack rate - proportion of population that develops illness.
Infant mortality rate - number of deaths among infants ages 0-1 year during a specified time period divided by the number of live births in the same time period.
Case - a person in a population with a particular disease, disorder or condition that is being investigated.
Rate - a measure of the frequency with which an event occurs in a defined population over a specified period of time.
Cause-specific death rate - the mortality rate from a specified cause for a population.
Incidence rate - the ratio of the number of cases to the total time the population is at risk of disease.
Prevalence rate - is the proportion of persons in a population who have a particular disease or attribute at a specified point in time or over a specified period of time.

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