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: Dental
All of the following are true regarding point source epidemic except _____. 
Select and explain. 
A. No secondary waves., B. Clustering of cases within a short period of time., C. Only due to an infectious agent., D. All cases usually develop within one incubation period.
C: Only due to an infectious agent.
Answer: C: Only due to an infectious agent. 
Explanation: Point source epidemics:

Belong to common source type of epidemics.
Also called single exposure epidemics.
All cases develop within one incubation period.
In epidemic curve, there is sharp rise and fall as all cases are clustered within one incubation period and there are no secondary waves.  
Not only infectious agents but , environmental pollution and contamination of food can also cause point epidemics