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
What is the first case of a paicular condition that comes to notice of a physician termed as? 
Select and explain. 
A. Primary case, B. Secondary case, C. Index case, D. Refer case
C: Index case
Answer: C: Index case 
Explanation: Index case is the first case that comes to the attention of the investigator. Case is defined as a person in the population or study group identified as having the paicular disease, health disorder or condition under investigation. - Primary case: It is the first case of a communicable disease introduced into the population unit being studied. - Secondary case: are those developing from contact with a primary case.