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What is The first case introduced into the population group to be studied is called: and explain in detail?
Ans: b (Primary case) Ref: Park, 19th ed, p. 90The term primary case refers to the first case of a communicable disease introduced into the population unit being studied.The term index case refers to the first case to come to the attention of the investigator; it is not always the primary case. Secondary cases are those developing from contact with primary case.