Out of the 75 persons who attended the picnic, 46 subsequently developed gastroenteritis.

**Tasks:**

- Calculate the attack rate?
- Draw an appropriate epidemic curve.
- Is this a primary or a secondary attack rate?
- Is this an incidence of prevalence rate?

**Solution:**

**1) ****Calculation**

Attack rate = number of exposed people infected with the disease divided by the total number of exposed people

Thus attack rate = 46/75 x 100 = 61.33%

**2) **Epidemic curve :

**3) **It is primary attack rate

**4) **It is an incidence rate