Stroke risk from multiple risk factors combined with hypertension: A primary care based case control study in a defined population of northwest England

PURPOSE: To examine how hypertension interacts with ether known risk factor s in affecting the rick of stroke in a primary care based setting. METHODS: Cases were patients with first-ever stroke identified from the com munity-based stroke register in 1994-95 in northwest England. Two controls per case wore randomly selected from the same primary care site and matched by age and sex. Information on predefined risk factors was extracted from medical records. RESULTS: 267 cases and 534 controls were included. Adjusted odds ratio (OR) for stroke from hypertension was 2.6 (95%, confidence interval: 1.7-3.9). In hypertensives who were current smokers, risk of stroke was increased 6 f old (OR = 6.1 (2.7-13.7)) as compared to non-smokers without hypertension. Hypertensives who had a preexisting history of myocardial infarction or obe sity or diabetes had 3 fold higher risks of stroke. Subjects with hypertens ion and with a history of transient ischemic attack or atrial fibrillation had greater than or equal to 8 fold excess risk of stroke. Among them, the risk was greater in those with poorly controlled or untreated hypertension (OR = 13.2 (2.6-67.0)) and in those with well or moderately controlled (OR = 5.2 (1.6-17.2)) as compared to subjects without both risk factors. There appeared to be a steady increase in rick of stroke according to the number of risk factors present, particularly in hypertensive subjects. CONCLUSIONS: Stroke risks in hypertensives associated with combinations of other risk factors appeared to follow an additive model. Subjects with mult iple risk factors should he targeted in order to reduce the overall risk fo r stroke. Ann Epidemiol 2000;10:380-388. (C) 2000 Elsevier Science Inc. All rights reserved.