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Viral Epidemiology: Basics
• Epidemiology is the study of the distribution and determinants of health‐related states or events (including disease), and the application of this study to the control of diseases and other health problems1.
• Various methods can be used to carry out epidemiological investigations: surveillance and descriptive studies can be used to study distribution; analytical studies are used to study determinants1.
Viral Epidemiology: Basics
• Prevalence2: is the proportion of a population who have a specific characteristic in a given time period.
• To estimate prevalence, researchers randomly select a sample (smaller group) from the entire population they want to describe. Using random selection methods increases the chances that the characteristics of the sample will be representative of (similar to) the characteristics of the population.
• For a representative sample, prevalence is the number of people in the sample with the characteristic of interest, divided by the total number of people in the sample.
# of people in sample with characteristic
• Prevalence = ━━━━━━━━━━━━━━━━━━━
Total # of people in sample
• To ensure a selected sample is representative of an entire population, statistical ‘weights’ may be applied. Weighting the sample mathematically adjusts the sample characteristics to match with the target population.
• Prevalence may be reported as a percentage (5%, or 5 people out of 100), or as the number of cases per 10,000 or 100,000 people. T
• Point prevalence is the proportion of a population that has the characteristic at a specific point in time.
• Period prevalence is the proportion of a population that has the characteristic at any point during a given time period of
interest. “Past 12 months” is a commonly used period.
• Lifetime prevalence is the proportion of a population who, at some point in life has ever had the characteristic.
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