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)