This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
Index case refers to 
Select and explain. 
A. First case of a communicable disease introduced into the population unit being studied, B. First case to come to attention of investigator, C. Developing from contact with primary case, D. An individual who has signs and symptoms connected to the suspected pathogens
B: First case to come to attention of investigator
Answer: B: First case to come to attention of investigator 
Explanation: First case of a communicable disease introduced into the population unit being studied Primary case First case to come to attention of investigator Index case Developing from contact with primary case Secondary case An individual who has signs and symptoms connected to the suspected pathogens Suspect case