<prompt> Index case is the -First case in a communityCase getting infection from primary caseCase getting infection from secondary caseFirst case detected by investigator  <response>: Ans. is d i.e., First case defected by investigator Ref: Park 22nde d. 92 21ste p. 91o Primary caseo Index case--First case of communicable disease introduced into the population.First case to come to attention of the investigator.o It is not always necessary that primary case will be index case : -When the first case noticed by the investigator is also the first case of the population - Primary case and index case are the same.When the first case nociced by the investigator is not the first case of the population primary case - Index case and primary case are different.o Secondary cases - Cases those developing from contact with primary case. 