<prompt> False statement regarding point source epidemic is:Many secondary wavesCases occur in clustersAll cases occur within one incubation periodRapid rise and fall  <response>: Ref: Parks Textbook of Preventive and Social Medicine,22nd edition. Page 62Explanation:Types of EpidemicsCommon source epidemicPropagated epidemicSlow Modern epidemicPoint source2 Multiple exposure1 Person to person2 Arthropod vector3 Animat reservoir POINT SOURCE EPIDEMICCommon exposure.Single source epidemic.Cases clustered around the source.Incubation period is same since time and source are same.All cases develop within single incubation period.No secondary waves since single source and at the same time.Point source epidemic is:o Explosive Clustering of cases within narrow- interval of timeo Rises rapidlyo Falls off rapidlyo Only single peako No secondary waves.Median incubation period: Time required for 50 of cases to occur following exposure.Examples:o Bhopal gas tragedyo Minamata disease in Japano Chernobyl tragedy.Epidemic Curve of Point Source EpidemicPROPAGATED EPIDEMICMost often infectious in origin.Person to person transmission possible e.g. hepatitis A. Polio.Does not occur in single incubation period.Gradual rise and fall.No single peak - Secondary waves are always present.Depends on:o Herd immunityo Contact statuso Secondary attack rate.ExamplesA. Continuous or Repeated ExposureWomen with genital herpes having multiple sexual partners.A well with contaminated water.B. Propagated EpidemicEpidemic of cholera.Epidemic of hepatitis A.Propagated Epidemic Curve 