All of the following are true regarding point source epidemic except _____.

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