By Wouter I. Schievink, MD; Mary Riedinger, RN, PhD; Tajinder K. Jhutty, RN, MSN, ACNP and Paul A. Simon, MD, MPH

Subarachnoid hemorrhage (SAH) due to the rupture of an intracranial aneurysm is an important cause of premature death and disability in the United States [1]. It has been estimated that between 1 and 12 million Americans have an intracranial aneurysm and each year approximately 27,000 Americans suffer an aneurysmal SAH. One-half of patients with aneurysmal SAH are dead within one month of the event and more than one-third of those who survive have major neurologic deficits. The etiology and pathogenesis of intracranial aneurysms are poorly understood but it is known that these are acquired lesions and both genetic and environmental risk factors have been identified. Differences in SAH incidence and mortality between racial groups have been demonstrated [2-12], but no information is available about the impact of SAH among the main racial groups within the same community or by socioeconomic status. We therefore investigated SAH in Los Angeles County, California, a large multiracial community.

Los Angeles County is a unique multiracial community in southern California. The County spans more than 4000 square miles and incorporates 88 cities. Ninety-nine percent of the population resides in urban settings. The population in Los Angeles County was 8.8 million in 1990, with 41% whites, 38% Hispanics, 11% blacks, and 10% Asians. The great majority of Hispanics were of Mexican (76%) or Central American (14%) origin. Among Asians, 26% were of Chinese origin, 23% of Filipino origin, 15% of Korean origin, and 14% of Japanese origin.

Mortality rates of spontaneous SAH were calculated from death certificate data provided by the L.A. County's Department of Health for the years 1985 to 1998. Deaths with a primary International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM) code of 430 were considered aneurysmal SAH deaths. Patients were classified by race, age group, and sex. Race was classified as non-Hispanic white (white), non-Hispanic black (black), Hispanic and Asian/Pacific Islander (Asian). Rates were calculated using 1990 census data for Los Angeles County and expressed as rates per 100,000.

Using the 1990 census data, we classified the 270 residential postal zones (ZIP codes) in Los Angeles County by median annual household income into three strata containing 90 ZIP codes each. Individual ZIP code regions ranged in population size from 29 to 99420 residents with a median of 30377 residents. ZIP code-level median household incomes ranged from $4999 to $31277 in the low-income stratum, $31560 to $42109 in the middle income stratum, and $42144 to $113277 in the high-income stratum. Death certificates contained information on ZIP codes from the years 1989 through 1998.

The total number of reported SAH deaths was 2911. Of these 2911 deaths, 2897 (99.5%) were used for the analyses; fourteen were excluded from the analyses due to incomplete data or small racial group sample size (Native Americans n=6, others n=7, and unknown n=1).

The overall SAH mortality rate was 2.5 per 100,000 per year, increasing from 0.1 for those younger than 20 years of age to 9.5 for those older than 70. The age-adjusted SAH mortality rate was 1.9 in whites, 2.7 in Hispanics, 3.0 in Asians, and 3.7 in blacks (Figure 1).

We observed an obvious age-race interaction (Figure 2). In those younger than 70 years of age, the SAH mortality rate among blacks was 2.2 that of whites and 1.8 that of Hispanics and Asians. Only in blacks did the SAH mortality rate decline after age 70 and in this age group the rate in blacks was lower than that in Asians or Hispanics and approaching the low rate in whites. The decline in SAH mortality rate after age 70 was seen both in black women and men. Until age 50, the SAH rate was remarkably similar among whites, Hispanics, and Asians, but after age 50 a disproportionate increase was found among Hispanics and particularly Asians compared to whites.

The SAH rates were higher in women than in men, particularly after age 50, and the sex ratio was very similar among the four racial groups (Figure 1 & Figure 3). The SAH rate was the highest in Asian women age 70 and older (23.5 per 100,000) (Figure 4). The mean age at death for all patients was 57.1 years. The mean age at death was 52.1 years for Hispanics, 53.0 years for blacks, 60.0 years for Asians, and 60.7 years for whites. The mean age at death was higher in women (59.4 years) than in men (53.1 years).

Information on ZIP codes was available for 98% (1951/1993) of death certificates for the years 1989 through 1998. An inverse relationship was observed between income and overall SAH mortality rates, with the rate falling from 2.8 among the low income group to 2.3 in the middle income group and 1.5 in the high income group. This relationship was observed among blacks, Asians, and Hispanics, but not in whites (Figure 5).

The U.S. minority population is growing rapidly, particularly in California [13-15]. Los Angeles County is the most ethnically diverse local jurisdiction in the US, with Hispanic residents now outnumbering whites, and Asians outnumbering blacks.

Marked racial differences in SAH mortality were found in our study. Overall, whites were at the lowest risk, Hispanics and Asians at intermediate risk, and blacks at the highest risk. Among the young and middle-aged, blacks were at a much higher risk of dying from a SAH than whites, Hispanics, or Asians. Unlike these other races, however, the SAH mortality rate decreased in blacks after age 70. With increasing age, SAH mortality increased more rapidly in Asians and Hispanics than in whites and elderly Asian women were at particularly high risk.

The reasons for these racial disparities in SAH mortality are not clear. Differences in the burden of certain risk factors are often implicated in differences in cardiovascular disease incidence among racial groups. In order of importance, the established risk factors for SAH are cigarette smoking, hypertension, and excessive alcohol use [1, 16, 17]. Among the population of Los Angeles, the prevalence of cigarette smoking in 1997 ranged from 16 to 20 percent across all racial groups, but 8 percent of whites consumed a pack or more per day compared to only 2 to 4 percent for the other racial groups [18]. Elderly Asian women, the group with the highest SAH mortality rate, had the lowest frequency of cigarette use. Diagnosed hypertension was most prevalent among blacks, intermediate among whites, and lowest among Hispanics and Asians [19]. Hispanics had the highest frequency of binge drinking, although the overall prevalence of alcohol use was highest among whites [20]. Thus, differences in the burden of established risk factors only can explain a small portion of the racial disparities in our study.

Socioeconomic factors could account for some of the racial differences found in our study. For example, low socioeconomic status is associated with poor access to health care services, poor nutrition, a lifestyle that promotes health risk behaviors, and environmental factors that may lead to increased rates of disease [21]. Using factors such as income, educational attainment, and employment status, Hispanics have the lowest socioeconomic status in Los Angeles County, blacks and Asians an intermediate socioeconomic status, and whites the highest socioeconomic status. Hispanics have a lower SAH mortality rate than blacks but the "healthy migrant effect" in Hispanics could have partially negated the socioeconomic disadvantages [22, 23]. Using income per ZIP code as a surrogate measure of socioeconomic status, an inverse relationship between socioeconomic status and SAH mortality rates was found in all racial groups except for whites. Thus, the racial disparities we observed in our study can, at least in part, be explained by differences in socioeconomic status.

Genetic factors play an important role in the etiology and pathogenesis of aneurysmal SAH [24, 25]. However, a genetic defect, such as in the type III procollagen or polycystin genes, can be demonstrated in less than 5% of patients with aneurysmal SAH. Other, more common, aneurysm susceptibility genes remain to be identified [26]. Some of these genes may be more prevalent among certain racial groups explaining the racial differences found in our study. For example, cerebral cavernous angiomas, another type of hemorrhagic cerebrovascular disease, have been linked to several genetic loci and one of those is particularly prevalent among the Hispanic population [27-29].

The decrease in SAH mortality we observed among elderly blacks has also been detected in mortality from cardiovascular disease in general and from intracerebral hemorrhage. This has been attributed to the mechanism of "survival of the fittest" [30]. In the Northern Manhattan Stroke Study, a decrease in intracerebral hemorrhage mortality among the elderly was seen in blacks as well as in Hispanics [9]. In our study, this particular age-race interaction for SAH was observed only in blacks and not in Hispanics. In a study from Cincinatti, no decrease in the SAH incidence was observed among elderly blacks but the number of patients in this age category was very small [5]. Our study has several limitations. First, we studied SAH mortality rates and it is not known whether the differences we observed were due to differences in incidence or case-fatality rates. The few studies that have compared case-fatality rates for SAH among racial groups have found very similar rates, [5-7, 11], indicating that differences in the incidence rates are the most likely explanation for the differences in the mortality rates we observed. Second, in our analysis only death certificate data were used and a careful review of all patient data was not performed. However, coded discharge diagnoses for SAH have a very high specificity and are much more accurate than any other type of stroke. Third, the categorization into four main racial groups that we used in our study does not reflect the heterogeneity of the population with mixed backgrounds. However, this simplified racial categorization should have weakened any of the associations we found in our study.

In conclusion, our study shows that among the young and middle-aged, blacks are at a much higher risk of dying from a SAH than whites, Hispanics, or Asians. Unlike these other racial groups, the SAH mortality rate decreases in blacks after age 70. With increasing age, SAH mortality increases more rapidly in Hispanics and Asians than in whites and elderly Asian women are at a particularly high risk. The racial disparities could partially be explained by differences in socioeconomic status

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