Background: It is hypothesized that the incidence of subarachnoid hemorrhage (SAH) is decreasing due to a reduction in risk factors and more aggressive treatment of unruptured cerebral aneurysms, but long-term data from broadly representative populations are lacking.
Methods: We assessed temporal trends in rates of hospitalization for SAH by using the 1994 to 2013 releases of the National Inpatient Sample (NIS), which provides data on a 20% nationally representative sample of U.S. hospitalizations. We used previously validated International Classification of Diseases, 9th Revision, Clinical Modification codes to identify hospitalizations for nontraumatic SAH. As a comparison, we also identified ICH hospitalizations since ICH shares many risk factors with SAH but is not generally amenable to preventive intervention such as aneurysm coiling or clipping. Population estimates from the U.S. census were used to calculate annual hospitalization rates per 10,000 persons. Rates were age-standardized to the 1994 U.S. general population, and linear least-square error trendlines were generated to facilitate comparisons between trends. Survey weights provided by the NIS were used to calculate nationally representative estimates.
Results: During the study period, 1,862,545 patients were hospitalized with SAH and 2,292,292 patients were hospitalized with ICH. From 1994 through 2013, the age-standardized hospitalization rate for SAH declined from 5.6 (95% confidence interval [CI], 5.1-6.1) to 3.3 (95% CI, 3.1-3.6) hospitalizations per 10,000 U.S. residents. The age-standardized hospitalization rate for ICH also declined, from 6.4 (95% CI, 6.0-6.7) to 5.1 (95% CI, 4.9-5.4) hospitalizations per 10,000 individuals. Temporal trends were similar for SAH and ICH (Figure).
Conclusions: We found that hospitalization rates for both SAH steadily declined in the U.S. over the past 2 decades. This was mirrored by a similar decrease in ICH hospitalizations.