Hepatitis A, Restaurant Example
Several patients were diagnosed with Hepatitis A. The local Restaurant A was thought to be the source of the infection. 40 case patients and a similar disease free group of control were contacted to determine if they ate at Restaurant A.
Odds of exposure in cases = a÷c = 30 ÷ 10 = 3
Odds of exposure in controls = b÷d = 36 ÷ 70 = 0.51
Odds Ratio = Odds of exposure in cases ÷ Odds of exposure in controls = 3 ÷ 0.51 = 5.83
This means that people who ate at Restaruant A were 5.8 times as likely to develop Hepatitis A than were people who did not eat there.