Objective: To evaluate whether changing the seizurefree interval in Arizona from 12 months to 3 months affected the number of seizure-related motor vehicle crashes. Methods: We performed a time trend study with analysis of motor vehicle crash reports in the state of Arizona 3 years before (1991-1993) and 3 years after (1994-1996) the seizure-free interval was decreased from 12 to 3 months. The number of motor vehicle crashes related to seizures, other medical conditions, and other nonmedical crashes was compared before and after the law changed. Other population trends, including population growth, registered vehicles, and registered drivers, are also reported. Results: Seizure-related crashes increased from 125 to 136 for the 3 years before and 3 years after the law changed, respectively. The total rate of seizure-related crashes did not increase on the basis of an incidence rate difference of -0.03/109 miles (95% confidence interval [CI], -0.30 to 0.24) and a relative risk of 0.98 (95% CI, 0.77 to 1.24). Over the same time interval, crashes related to other medical conditions increased from 288 to 310, respectively, for an incidence rate difference of -0.09/109 miles (95% CI, -0.51 to 0.33) and a relative risk of 0.97 (95% CI, 0.82 to 1.13). Fatalities due to seizure-related crashes decreased during the same period, whereas the number of multiple vehicle crashes increased. Conclusion: The rate of seizure-related crashes did not significantly increase in the state of Arizona after the seizure-free interval was reduced from 12 to 3 months.
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