INCIDENCE PREVALENCE.pptx

Epidemiology

1. INCIDENCE PREVALENCE

2. What is incidence? The rate at which new events occur in a defined population during a specified period of time.

3. Numerator Denominator Multiplier Number of NEW events in a specified period X n 10 The numerator strictly refers only to first events of disease.

4. Example: In a village, total population is 30000 & new cases of a disease are 300. Calculate Incidence rate of disease.

5. Attack rate Its an Incidence rate. Expressed as a percentage. Used when population is exposed to risk for limited period of time, like in epidemic. Attack rate= No. of new cases of specific diseases during specified time interval * 100 Total population at risk during same interval

6. Secondary attack rate Definition: No. of exposed persons developing the disease within the range of the incubation period following exposure to a primary case.

7. Formula:

8. Calculation: Family of 6 people, consisting 2 parents. 4 children, who are susceptible to a disease measles. There is one case in family & within short time 2 secondary cases among remaining children. Calculate Secondary attack rate.

9. CUMULATIVE INCIDENCE/ INCIDENCE DENSITY

10. When calculating incidence, those having the disease in the population at the start or baseline need to be identified and excluded from the denominator

11. Prevalence The number of people with a disease. No of all current cases ( old + new) existing during a defined period of time. Prevalence is most often expressed as a proportion. Formula-

12. Point Prevalence & Period Prevalence

13. Prevalence and incidence incidence recovery death Point prevalence is the balance between inflow to the prevalence pool (incidence) and outflow (e.g. r ecovery and/or mortality).

14. The relationship between incidence and prevalence PREVALENCE = INCIDENCE X DURATION

15. Calculation: In a village, total population is 30000 & new cases of a disease are 300 & old cases are 300. Calculate Prevalence of disease.

16. Calculation: In population of is 1000 incidence of a disease is 100 in one year. Disease studied for 2 years. Calculate Prevalence of disease.

17. Calculation: In 2009, in one village , total population is 1450, of which 130 were asthma cases . In 2010, out of 1370 population in same village , total 130 asthma cases were there. Of which 42 were first time diagnosed & 88 had been previously diagnosed. Calculate prevalence rate of asthma in 2009 & 2010 separately. Calculate incidence rate of asthma in 2010.