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
[{'content': 'In an epidemiological study, the first case whichcomes to the attention of the investigator is \nSelect and explain. \nA. Reference case, B. Index case, C. Primary case, D. Secondary case', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 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.', 'role': 'assistant'}]