Which of Koch's postulates describes why multiple students have similar symptoms and the same test results, while others have had no symptoms and are probably not infected?
1) Postulate 1: The microorganism must be present in every case of the disease.
2) Postulate 2: The microorganism must be isolated from the diseased host and grown in pure culture.
3) Postulate 3: The cultured microorganism should cause disease when introduced into a healthy organism.
4) Postulate 4: The same microorganism must be re-isolated from the newly infected host.