Case ascertainment and diagnosis of stroke in an epidemiologic study: The Shibata stroke study

Abstract

Beginning in 1976, an epidemiologic study of stroke has been under way in the City of Shibata, Niigata Prefecture, Japan. The study's methodology of case ascertainment and the accuracy of diagnosis (clinical judgement), according to patient histories, and general and neurological physical examinations are reported. In order to ascertain all new stroke patients in Shibata, a surveillance system was employed. The system included annual mass-examination, and referrals by all general practitioners in the Shibata area, the Niigata Prefectural Shibata Hospital, a private mental hospital and a nursing home. Suspected patients were also referred by the 12 visiting public health nurses by a laymen's association for stroke control, and by the nearby Kita-Kambara County Hospital. The records of the Division of Emergency Services of the Shibata Fire Department and the social insurance records were also regularly reviewed by a physician of the study team. Information about fatal strokes was obtained by review of all death certificates, with supplementary clinical data obtained from the individual certifying physician. All patients alive at the time of referral were examined by a physician of the study. If the patient was dead, clinical information was collected from the relatives of the patient and the certifying physician. The information obtained from examinations and a review of the records was entered on a standard form and was evaluated by a group of three staff physicians to determine if the patient met the criteria as a stroke case. If so, an attempt was made to diagnose the anatomical type of stroke. Since more than 60% of the stroke patients were diagnosed only on the basis of clinical judgment, the accuracy of this method was estimated using 143 stroke patients and 48 non-stroke patients admitted to a special hospital for stroke in Osaka. If clinical judgment was made by a group of three physicians, 97.2% of the patients confirmed to have had stroke by computed tomography and other procedures, and 97.9% of those confirmed as not having had stroke were so designated by the clinical judgment. Of the 19 subarachnoid hemorrhages, 68.4% were diagnosed correctly using clinical judgment alone, as were 86.0% of the 49 cerebral hemorrhages and 82.4% of the 75 cerebral infarctions. Thus it is concluded that clinical judgment by a group of three physicians is an adequate method to identify stroke cases.