All are true for Point source epidemic except:
EPIDEMIC:

Definitions of epidemic:

– Occurrence of no. of cases of a disease ‘clearly in excess of normal expectancy (NE)’

Normal expectancy is derived by looking at average of no. of cases of the disease in previous 3 – 5 years in that geographical area
If NE = zero, ‘even one case is considered epidemic’

– Statistically speaking, epidemic is when no. of cases ‘exceed twice the standard deviation’
No. of cases > Mean + 2SD ( >μ + 2σ)
– Occurrence of a new disease in a population (as NE = Zero)
– Reoccurrence of an eliminated/ eradicated disease in a population (as NE = Zero)
Person-to-person transmission
Clustering of cases within a short period of time
Epidemic curve rises and falls sharply
All cases usually develop within one incubation period