Blood-clot-related strokes decrease among whites, but not blacks, in long-term study

May 20, 2010

The incidence of blood clot-related strokes fell among whites in the Greater Cincinnati/Northern Kentucky area for the first time, according to long-term surveillance study representative of strokes in blacks and whites nationwide reported in Stroke: Journal of the American Heart Association.

However, there was no decrease in stroke rates among blacks.

"It's encouraging that, for the first time ever in our study area, there is a drop in the most common type of stroke," said Dawn Kleindorfer, M.D., lead author of the study and assistant professor of neurology at the University of Cincinnati. "However, it's very disappointing that the racial disparity seems to be getting worse."

Investigators found that the age-adjusted annual rate of (those caused by a blood clot) resulting in hospitalization changed between 1999 and 2005 from:

  • 189 to 167 per 100,000 overall, an 11.6 percent drop;
  • 180 to 154 per 100,000 among whites, a 14.4 percent reduction;
  • 263 to 275 per 100,000 among blacks, a 4.6 percent rise, but not a significant change.
The patterns remained the same when out-of-hospital strokes were included. During the same period, researchers found no change in the rate of hemorrhagic strokes (those caused by bleeding).

The likelihood of dying after an ischemic stroke remained steady over time and was similar in whites and blacks, about 10 percent, according to the report.

Researchers used data from the Greater Cincinnati/Northern Kentucky Stroke Study, which gathered information on all first strokes occurring in a five-county area with 1.3 million people. The counties include urban, suburban and rural areas. It's comparable to the nation in education, income and in the percentage of blacks (18 percent), but does not include a substantial proportion of persons of Hispanic ethnicity (less than 3 percent).

"When you look at national maps on mortality, you see many more stroke deaths in blacks," Kleindorfer said. "According to our data, this occurs because blacks are far more likely to have a stroke to begin with, not because they are more likely to die once the stroke happens."

The racial disparity could not be explained by differences in the occurrence and treatment of stroke risk factors. According to a telephone survey conducted in the study area, blacks were more likely than whites to have been diagnosed with risk factors such as high blood pressure and diabetes, but they were also more likely to be receiving treatment for these conditions.

"We've done a lot of work in the community to increase stroke awareness and encourage prevention, but the stroke rates are absolutely stable in blacks," Kleindorfer said.

The investigators are collecting 2010 data in their ongoing phase of their epidemiology of project.

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