In an epidemiological study, the first case whichcomes to the attention of the investigator is
Index case Epidemiological terminology Primary case - is the _first case of a communicable disease introduced into the population unit under study. Index case - is the first case, that comes to the attention of the investigator, it is not always the primary case. Secondary cases - are those cases arising d/t contact with the primary case.
Reference case
Index case
Primary case
Secondary case