Infectivity of an organism is measured by

Infectivity of an organism is measured by incidence rate Incidence rate: It is the number of new cases occuring in a defined population during a specified period of time Prevalence rate: It is the number of new and old cases existing in a population during a specified period of time Case fatality rate: It is the ratio of total number of deaths due to a paicular disease to total number of cases due to same disease Secondary attack rate: It is defined as the number of exposed person developing the disease within the range of the incubation period following exposure to a primary case Ref : Park&;s Textbook of preventive and social medicine; 24th edition; Pg no 60