This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Time Distribution, Epidemics, Subject name: Social & Preventive Medicine
The area is declared free of epidemic: 
Select and explain. 
A. Till last secondary case recovers, B. No new case repoed for the incubation period of disease since the last case, C. No new case repoed for twice the incubation period of disease since the last case, D. No new case repoed for six months since the last case
C: No new case repoed for twice the incubation period of disease since the last case
Answer: C: No new case repoed for twice the incubation period of disease since the last case 
Explanation: Epidemic: Number of cases of a disease clearly in excess of normal frequency. An area is declared free of epidemic; if on search , no new cases are repoed for 'twice the incubation period of the disease since the occurrence of last case'.