Abstract

Background and Purpose: To update our 1996 review on the incidence of subarachnoid haemorrhage (SAH) and assess the relation of incidence with region, age, gender, and time period.

Methods: We searched for studies on incidence of SAH published until October 2005. The overall incidences with corresponding 95% confidence intervals (CI) were calculated. We determined the relationship between the incidence of SAH and determinants by means of univariable Poisson regression.

Results: We included 51 studies (33 new), describing 58 study populations in 21 countries, observing 45.821.896 person-years. Incidences per 100.000 person-years were 22.7 (95%CI 21.9 to 23.5) in Japan, 19.7 (18.1 to 21.3) in Finland, 4.2 (3.1 to 5.7) in South and Central America, and 9.1 (8.8 to 9.5) in the other regions. With age-category 45 to 55 as reference, incidence ratios increased from 0.10 (0.08 to 0.14) for age groups younger than 25 years to 1.61 (1.24 to 2.07) for age groups older than 85. The incidence in women was 1.24 (1.09 to 1.42) times higher than in men; this gender difference started at age of 55, and increased thereafter. Between 1950 and 2005 the incidence decreased with 0.6% (1.3% decrease to 0.1% increase) per year.

Conclusions: The overall incidence of SAH is around 9 per 100.000 person-years. Rates are higher in Japan and Finland and increase with age. The preponderance of women starts only at the sixth decade. The decline in incidence of SAH over the past 45 years is relatively moderated compared to that for stroke in general.