Editors' Note: Substantial Within-Country Variation in the Incidence of Subarachnoid Hemorrhage: A Nationwide Finnish Study

Abstract

In “Substantial Within-Country Variation in the Incidence of Subarachnoid Hemorrhage: A Nationwide Finnish Study,” Rautalin et al. reported that data from the nationwide Causes of Death and Hospital Discharge Registers in Finland demonstrated that the incidence of subarachnoid hemorrhage (SAH) between 1998 and 2017 varied by region, and although it decreased across regions during the study period, the rate of decrease varied significantly by region. Frösen et al. noted concern about the integrity of the administrative database used in this study because they did not observe a decreased number of hospitalized patients with aneurysmal SAH from 1990 to 2014 in their hospital. However, they also proposed that this discrepancy could be attributed to a decrease in out-of-hospital mortality associated with aneurysmal SAH from 1998 to 2000 and 2015 to 2017 because this would decrease the incidence rates reported from hospital discharge and death registries without affecting admission and observational data. Rautalin et al. confirmed that this hypothesis was correct by analyzing the sudden death rate from SAH within the hospital's catchment area during the study period and reporting a decrease from 28% to 18%; they also found that the percentage of patients with SAH admitted to other hospitals in the area during the study period decreased from 17% to 4%. They conclude that the comparison between the data from the administrative database and the hospital-based data demonstrates how hospital-based studies can underestimate epidemiology of SAH because they do not account for out-of-hospital deaths or patients who are managed in the outpatient setting. Limitations to epidemiology studies using both administrative and hospital-based data must be acknowledged. In “Substantial Within-Country Variation in the Incidence of Subarachnoid Hemorrhage: A Nationwide Finnish Study,” Rautalin et al. reported that data from the nationwide Causes of Death and Hospital Discharge Registers in Finland demonstrated that the incidence of subarachnoid hemorrhage (SAH) between 1998 and 2017 varied by region, and although it decreased across regions during the study period, the rate of decrease varied significantly by region. Frösen et al. noted concern about the integrity of the administrative database used in this study because they did not observe a decreased number of hospitalized patients with aneurysmal SAH from 1990 to 2014 in their hospital. However, they also proposed that this discrepancy could be attributed to a decrease in out-of-hospital mortality associated with aneurysmal SAH from 1998 to 2000 and 2015 to 2017 because this would decrease the incidence rates reported from hospital discharge and death registries without affecting admission and observational data. Rautalin et al. confirmed that this hypothesis was correct by analyzing the sudden death rate from SAH within the hospital's catchment area during the study period and reporting a decrease from 28% to 18%; they also found that the percentage of patients with SAH admitted to other hospitals in the area during the study period decreased from 17% to 4%. They conclude that the comparison between the data from the administrative database and the hospital-based data demonstrates how hospital-based studies can underestimate epidemiology of SAH because they do not account for out-of-hospital deaths or patients who are managed in the outpatient setting. Limitations to epidemiology studies using both administrative and hospital-based data must be acknowledged.