This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
All are true for Point source epidemic except 
Select and explain. 
A. Epidemic curve rises and falls sharply, B. Clustering of cases within a short period of time, C. Person-to-person transmission, D. All cases usually develop within one incubation period
C: Person-to-person transmission
Answer: C: Person-to-person transmission 
Explanation: EPIDEMIC:
• Definitions of epidemic:
– Occurrence of no. of cases of a disease ‘clearly in excess of normal expectancy (NE)’
1. Normal expectancy is derived by looking at average of no. of cases of the disease in previous 3 – 5 years in that geographical area
2. If NE = zero, ‘even one case is considered epidemic’