You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Index case refer to:- and explain in detail?
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