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 In an epidemiological study, the first case which comes to the attention of the investigator is - and explain in detail?
Primary case refers to the first case of a communicable disease introduced into the first unit being studied. Index case is the first case which comes to the attention of the investigator. They may not always be the same. Ref: 25th edition, Park's Textbook of Preventive and Social Medicine, Page no. 103