1. Incidence rate (or person-time rate)
   1. Numerator
   2. Denominator
      1. Summed person-years of observation or average population during time interval
   3. Number of new cases of disease during specified time interval
2. Outbreak
   1. Primary attack rate
      1. Numerator
      2. Denominator
         1. Population at start of time interval
      3. Number of new cases of disease during specified time interval
   2. Secondary attack rate
      1. Numerator
         1. Number of new cases among contacts
      2. Denominator
         1. Total number of contacts
   3. Overall attack rate
      1. Numerator
         1. Total number of new cases divided
      2. Denominator
         1. Total population
3. Point prevalence
   1. Numerator
      1. Number of current cases (new and preexisting) at a specified point in time
   2. Denominator
      1. Population at the same specified point in time
4. Point prevalence
   1. Numerator
      1. Number of current cases (new and preexisting) at a specified point in time
   2. Denominator
      1. Average or mid-interval population
5. Herd immunity
   1. Occurs after the susceptible susceptible individuals are reduced to a critical number that prevents that reintroduction of the infection will not result in a new epidemic
6. epidemic
   1. Occurrence of disease that is temporarily of high prevalence
   2. Endemic
      1. An epidemic occurring over a limited geographical area (e.g., Dengue & Malaria are not developed in areas over 1600 mts height, because the mosquitoes are not able to live there)
   3. Pandemic
      1. An epidemic occurring over a wide geographical area (e.g., worldwide)
7. Incidence
   1. New cases of disease or injury in a population over a specified period of time
   2. Incidence proportion
      1. Measure of the probability (risk) of developing the disease during the specified period. When it is unexpected it is called Outbreak
8. Attack rate
   1. Primary
      1. Same as incidence proportion is the proportion of people who become ill with (or who die from) a disease in a population initially free of the disease.
   2. Secondary
9. Case definition
   1. Set of criteria to define the disease of interest
10. 1.Principles of Epidemiology. (2022). Retrieved January 9, 2022, from https://www.cdc.gov/csels/dsepd/ss1978/lesson3/section2.html 2. Dengue. (2022). Retrieved January 9, 2022, from https://www.cdc.gov/dengue/