This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
In an epidemiological study, the first case whichcomes to the attention of the investigator is 
Select and explain. 
A. Reference case, B. Index case, C. Primary case, D. Secondary case
B: Index case
Answer: B: Index case 
Explanation: 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.