The Epidemiology of Admissions of Nontraumatic Subarachnoid Hemorrhage in the United States

BACKGROUND: Subarachnoid hemorrhage (SAH) is the cause of 5% to 10% of strokes annually in the United States. OBJECTIVE: To study the incidence and mortality trends of admissions of SAH from 1979 to 2008 using a nationally representative sample of all nonfederal acute-care hospitals in the United States: The National Hospital Discharge Survey. METHODS: The sample was obtained from the hospital discharge records according to the International Classification of Disease, 9th Revision, Clinical Modification code 430. RESULTS: We reviewed data on approximately 1 billion hospitalizations in the United States over a 30-year study period and identified 612 500 cases of SAH, which was more common in women (relative risk 1.71, 95% confidence interval 1.7-1.72) and nonwhite persons than white persons (relative risk 1.46, 95% confidence interval 1.4-1.5). The estimated incidence rate of admission after SAH was 7.2 to 9.0 per 100 000/year and did not significantly change over the study period. Overall, in-hospital mortality after SAH fell from 30% during the period from 1979 to 1983 to 20% during the subperiod from 2004 to 2008 (P = .03) and was lower in larger treating hospitals. The average days of care for SAH hospitalizations decreased, but the rate of discharge to long-term care facilities increased. CONCLUSION: The incidence rate of admission after SAH has remained stable over the past 30 years. Total deaths and in-hospital mortality after SAH have decreased significantly. In-hospital mortality after SAH is lower in larger treating hospitals. ABBREVIATIONS: CI, confidence interval ICD-9-CM,International Classification of Disease, 9th Revision, Clinical Modification NHDS, National Hospital Discharge Survey RSE, relative standard error RR, risk ratio SAH, subarachnoid hemorrhage SE, standard error