Medical impairment and road traffic crashes among older drivers in Sweden - A national, population-based, case-control study.

BACKGROUND: Several medical conditions are known to impair sensory, cognitive and motor functions and are associated with road traffic crashes (RTC). For the drivers of today, we lack updated knowledge on how driving-impairing conditions are associated with RTCs, across all driving-impairing conditions in a given population. We aim to determine this among older drivers in Sweden.

METHODS: A national, population register-based, matched case-control study comparing acknowledged driving-impairing health conditions among all older drivers (65 years or older) involved in an injurious RTC in the period 2011-2016 (n = 13,701) with those of controls: older drivers not involved in any RTC (n = 26,525) matched to the cases by age, sex and residential area. The medical conditions, extracted from the National Patient Register from 1997 up until date of RTC, were identified based on ICD-10 diagnosis codes and categorized into the 13 groups of medical conditions listed in the Swedish driver's license regulations. Conditional logistic regression was used to estimate crude and adjusted odds ratios (ORs) with 95% confidence intervals.

RESULTS: Unadjusted ORs for RTC were increased for all conditions. After taking the other 12 medical conditions into account, the ORs remained significant in 11 out of the 13. A strong association was found for the group "ADHD and autism spectrum disorders" (OR 2.79, CI 1.47-5.30), although with very low prevalence among cases (0.2%). Moderate associations were found for three conditions with a case prevalence between 1.3% and 8.5%: epilepsy and seizure disorders (OR 1.53, CI 1.25-1.89), substance abuse and dependence (OR 1.45, CI 1.29-1.63), psychological diseases and mental disorders (OR 1.28, CI 1.18-1.39) and for one condition with a case prevalence of 14.7%, diabetes (OR 1.28, CI 1.20-1.36).

CONCLUSIONS: In Sweden, in the current generation of older drivers, acknowledged driving-impairing medical conditions at the national and European levels remain a concern. After adjustment for one another, all but 2 of the conditions are associated with RTCs albeit to varying degrees and more pronounced in the age group 65-79 compared to 80 or older. To promote and sustain older people's mobility, addressing this issue will require a blend of interventions where, hopefully, technological and infrastructural innovations may help counteracting individual health-related shortcomings.