Incidence of stroke in Switzerland

In the recent study, based on International Classification of Diseases (ICD)-10 discharge hospital stroke codes, Hansel et al. suggested a substantial burden of stroke in Switzerland with an increase in first and recurrent stroke incidence in Switzerland from 146.0/100 000 inhabitants in 2009 to 325.0/100 000 in 2017 [1, 2]. Here, we consider that these results should be interpreted with caution as they are markedly discordant with stroke incidence estimates recently reported in population-based studies in Switzerland and in other western European populations [3–5]. In our recent population-based study based on data collected in Geneva in 2018–9, the annual incidence of first and recurrent strokes was 158.4/100 000 in Switzerland when adjusted to the Swiss population [4]. The discrepancy between Hansel et al. and population-based studies is not anecdotal. Indeed, the annual number of strokes in Switzerland is 13 491 if we consider our population-based study, and 26 032 based on Hansel et al. study. In our recent Geneva study, each stroke patients’ charts were reviewed by board-certified stroke neurologists to ensure that they fulfilled the ICD-10 code of stroke. Since data from the Geneva hospital contributed to both the Hansel study and our population-based study, we are uniquely positioned to highlight important methodological issues that may explain the unexpectedly high stroke incidence reported by Hansel et al. [2].