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International Journal of Stroke 18(6)
Conclusion: The stroke incidence continued to decline in both urban and rural Japanese communities with the regional
disparities over the past half century, whereas it remained higher than that in many Western countries.
Keywords
Stroke, incidence, urban-rural disparities, trend, Asia, epidemiology
Received: 23 July 2022; accepted: 22 September 2022
Introduction
Stroke remains a major cardiovascular concern worldwide
because of its high mortality and contribution to healthy
life lost in stroke survivors with physical and mental disabilities.1
Asian countries such as Japan have had a higher
stroke burden than ischemic heart disease.2 Stroke was
once the primary cause of death among the Japanese population
from 1951 to 1980 and dropped to the fourth rank in
2018.3 Sustained improvements in the stroke epidemic
started in the mid-1960s, mainly attributable to community-based
prevention programs for hypertension, increased
coverage of antihypertensive medication use in patients
with hypertension, dietary education such as salt reduction
campaigns and balanced dietary guidelines, and strategies
for discouraging cigarette smoking.2
Special attention has been given to the urban-rural disparities
in stroke epidemiology because rural residents had
a higher prevalence of hypertension and other stroke risk
factors than urban residents.4 The urban-rural disparities
are reported previously.5,6 However, these studies about the
urban-rural disparities of stroke were performed with a
cross-sectional design, and few data have been published
comparing long-term trends in the stroke incidence between
urban and rural communities.
The Circulatory Risk in Communities Study (CIRCS) is
one of the frontier community-based epidemiological studies
in Japan,7 designed to investigate cardiovascular risk
factors and lead the community cardiovascular prevention
programs in both urban and rural communities since 1963.
This study design permitted comparing stroke incidence
based on unified public health interventions and surveillance
systems. A previous CIRCS reported declining trends
in the incidence of all strokes in urban and rural communities
between 1963 and 2003.7 Accordingly, the aim of this
study was to provide updated data including the incidence
of stroke subtypes and focus on the urban-rural disparities
in Japan.
Methods
Study population
This study comprised two Japanese communities in
which the CIRCS research team participated and led their
cardiovascular prevention programs since 1963/1964.
The Minami-Takayasu district of Yao city is an urban
International Journal of Stroke, 18(6)
community in Osaka Prefecture, mid-western Japan, with
a census population of 22,286 (of 268,983 in Yao city) in
2015. Ikawa town is a rural farming community located
in Akita Prefecture, northwestern Japan, with a census
population of 4986 in 2015. This study targeted residents
aged 40 years or older, which was different from the 40 to
69 years in the previous report of CIRCS.7 The population
of residents aged 40 years or older changed from
3242 (population density: 3242 residents/5.45 km2 = 595
residents/km2) in 1965 to 13,307 (2442 residents/km2) in
2015 for the urban community, and 2311 (population
density: 2311 residents/47.95 km2 = 48 residents/km2) to
3586 (75 residents/km2) for the rural community. The
Ethics Committees of Osaka Center for Cancer and
Cardiovascular Disease Prevention and Osaka University
approved this study, and informed consents were obtained
collectively from community representatives since this
study involved the secondary use of data obtained for
public health practice on cardiovascular disease prevention
in the local communities according to the guidelines
of the Council for International Organizations of Medical
Science.
Registration process and ascertainment of
stroke cases
Stroke registrations were conducted from the community
and local hospitals/clinics to avoid omissions of incident
cases. The surveillance sources of candidate cases included
annual household questionnaires, cardiovascular risk surveys,
death certificates (i.e. national death records), ambulance
records, national insurance claims, and reports from
local physicians, public health nurses, and health volunteers.
To validate the diagnoses, those with suspected stroke
were telephoned, visited, or invited to take part in a survey
to further confirm the diagnosis. For cases of death, medical
histories and records were obtained from the bereaved
families or attending physicians. The final diagnosis was
based on comprehensive medical records with standardized
case report forms reviewed by a team comprising experienced
physician epidemiologists. Stroke was defined as a
focal neurological disorder with a rapid onset that persisted
for at least 24 h or until death. Transient ischemic attacks
were ruled out accordingly.
Stroke subtypes were categorized as intracerebral hemorrhage,
subarachnoid hemorrhage, ischemic stroke, or
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