[Epidemiological study of the features of the index cases in SARS case clusters].

OBJECTIVE: To understand the epidemiological characteristics of the index cases in severe acute respiratory syndrome (SARS) cases clusters and to evaluate their importance in the whole epidemic process of SARS. METHODS: Data of the index SARS cases and the subsequent case clusters were collected by means of face-to-face interview in combination with field investigation and case history consultations. RESULTS: In all three SARS clusters, the index cases all had chronic disease and played the role of infection source that transmitted the virus to the patients' family members, attending medical staff as well as other non-SARS patients sharing the same ward with them. CONCLUSION: The index cases played an important role in transmission of SARS virus among the case clusters, and their infective stages are confined within certain phases of the disease course.