gms | German Medical Science

Objective: To investigate the time trends in the incidence of aneurysmal subarachnoid hemorrhage (SAH) with emphasis on region, age and sex by performing a systematic review and meta-analysis of population-based studies.

Methods: We updated our previously reported meta-analyses on SAH incidence published in 1996 and 2007 by performing a systematic review of the MEDLINE database until February 2015 using the key words (“subarachnoid hemorrhage” OR “subarachnoid haemorrhage”) AND (“incidence“ OR “epidemiology” OR “population”). Main inclusion criteria were: 1) prospective study design, 2) reported study population was representative of the specific population, with respect to age and sex distribution, 3) for studies on stroke incidence in general, SAH was reported as a separate entity, 4) reported data included or enabled the calculation of the crude SAH incidence, 5) case finding methods included all hospitals in the region and either involvement of general practitioners or review of death certificates during the study period. For region analysis 4 populations were defined: A) Reference (all regions except B-D), B) Finland, C) Japan, D) Middle/South America. Poisson regression analyses were performed to calculate crude and region specific SAH incidences with 95% confidence intervals (CI). Moreover we assessed temporal incidence trends with year of study as determinant and stratified these analyses by sex and adjusted for age.

Results: We included 101 studies (58 old, 43 new), describing 9,408 SAH patients in 71,511,325 patient-years from 32 countries. Between 1955 and 2011 the crude SAH incidence declined by 1.3% (95% CI: 1.0-1.6) per year in the reference population. The crude SAH incidence per 100,000 person-years was 9.4 (95% CI: 9.2-9.7) in the reference population; 24.2 (22.7-25.7) in Finland, 22.8 (20.1-23.5) in Japan, 4.3 (3.7-5.1) in Middle/South America. For studies which reported incidence data stratified by age and sex (21 studies; 1381 patients) the overall crude annual decrease was 1.4% (0.6-2.1), after adjustment for age 2.0% (1.2-2.8). In these 21 studies the annual decreases stratified by sex were: men crude 2.0% (0.8-3.2), men age adjusted 2.6% (1.3-3.8), women crude 0.8% (-0.2-1.9), women age adjusted 1.5% (0.4-2.5). Mean age in the new studies was 40.5 years versus 36.9 in the old ones, with an age-specific risk ratio per year of 1.07 (95% CI: 1.07-1.08) in the new studies versus 1.07 (95% CI: 1.06-1.08) in the old ones.

Conclusion: The overall incidence of SAH in populations excluding Finland, Japan and Middle/South America has annually declined by 1.4% over the past 7 decades and now constitutes 9.5 per 100,000 person-years; the SAH incidence in Finland and Japan continues to be distinctly higher, whereas in Middle/South America it remains distinctly lower than in the reference population. The overall crude decrease in SAH incidence is more pronounced in men than in women.