stroke - mortality rate - health inequalities
acidente vascular cerebral - mortalidade - desigualdades em saúde
Stroke is the second leading cause of death in Brazil and worldwide[1] and trends in stroke mortality rates may be analyzed as a proxy of social economic
differences among countries and regions. A systematic review of population-based studies
showed a divergent, statistically significant difference trend in stroke incidence
rates, from 1970 to 2008. It was observed a 42% decrease in stroke incidence in high
income countries in contrast to a more than 100% increase in this incidence in middle
and low income countries[2]. There is a ten-fold difference in mortality rates for stroke between the most-affected
and the less-affected countries. Moreover, national per capita income has been pointed
out as the strongest predictor of stroke mortality even after adjusting for cardiovascular
risk factors[3].
In Brazil, there is evidence of declining mortality from stroke in São Paulo since
the 1970s[4] and all over the country since the 1980s[5], but the magnitude of the mortality rates and its decline, as well as the differences
among the regions of the country need to be better investigated. From 1979 to 1996,
among Brazilian adults aged 30 or more years old, despite the high values, the age-adjusted
death rate for stroke dropped significantly (p<0.001) from 200 to 164 deaths/100,000
population in men and from 168 to 130 deaths/100,000 population in women[6].
Mortality is a measure of incidence of deaths in the total population at risk and
its frequency depends both on the incidence of the disease and its case-fatality ratio,
the proportion of death among those with the disease. Survival to stroke is highly
dependent on medical care, which seems to be improving in the country. In the beginning
of the ‘80s, a one-year study in all hospitals and emergency care units in the city
of Salvador revealed an extremely high 30-day case fatality rate (80.7%), probably
consequence of poor access to health preventive and medical facilities, mainly hypertension
care and emergence assistance[7]. In 2003-2004, the only two Brazilian population-based studies, in small cities
(75,000 inhabitants) of the states of Sao Paulo[8] and Santa Catarina[9], observed a 30-day case fatality rate of less than 20%, similar to that observed
in developed countries[2]. Among the population of Joinville city, compared with data from 1995, it was observed
around 30% decrease in incidence, mortality and 30-day case fatality ratio for stroke[9]. It is noteworthy that these estimates cannot be generalized to the whole country,
as these studies were performed in the two most developed Brazilian regions.
Stroke incidence can be prevented to a large extent by health policies toward reduction
of its main risk factors, as hypertension, diabetes, smoking, unhealthy diet and lack
of physical activity. Prevention of premature deaths is one of the main objectives
of health policies and declining trends on mortality and case fatality rates reflect
social and medical improvement over time.
In order to investigate if these good trends have come to stay, this work studies
the stroke mortality among the Brazilian adults up to now. Moreover, the stroke mortality
trends among the regions of the country are also evaluated, since inequalities may
be hidden by aggregate data.
METHOD
Deaths from all types of cerebrovascular disease were classified using the underlying
cause codes I60-I69 according to the International Classification of Diseases – Tenth
Revision (ICD-10). Data from all deaths that occurred between 1996 and 2011 among
individuals aged between 30 and 69 years were obtained from the Brazilian Mortality
Information System (SIM, Sistema de Informação sobre Mortalidade)[10], which provides underlying cause of death, date, local of death and selected characteristics
of deceased.
The crude number of notified deaths were corrected according to the following steps:
1) deaths with non-registered sex or age were reallocated pro-rata according to registered
sex and age; 2) redistribution of garbage codes, that is, deaths from all other ICD
chapters assigned to causes that cannot or should not be considered underlying causes
of death, by sex and region[1] and 3) redistribution of ill-defined causes of deaths (ICD 10 XVIII chapter)[11] ([Table 1]).
Table 1
List of garbage codes and the proportion of redistribution to cerebrovascular disease
as the cause of death.
|
Group of the garbage codes
|
ICD-10 codes*
|
Proportion (%)
|
|
Atherosclerosis
|
I70.0–I70.1, I70.9
|
53.90
|
|
Hypertension
|
I10, I15
|
28.67
|
|
Other and unspecified disorders of circulatory system
|
I99
|
25.68
|
|
Different paralytic syndrome/palsy syndrome
|
G80–G83
|
14.73
|
|
Diseases of the genitourinary system (C14)
|
N39.3, N40, N45–N46, N60, N84–N92, N95, N97
|
13.41
|
|
Osteomuscular system (C.13)
|
M10–M11, M15–M25, M40, M45, M47–M48, M50–M60, M65–M67, M70–M71, M75–M79, M95–M99
|
12.77
|
|
Mental, behavioral and neurodevelopmental disorders (C.5)
|
F30–F33, F34.1, F40–F48, F51–F53, F60–F99
|
10.92
|
|
Diseases of the blood and blood-forming organs and certain disorders involving the
immune mechanism (C3)
|
D10–D24, D26–D31, D35–D36
|
10.45
|
|
DIC, acute respiratory failure
|
D65, I46, J96.0, J96.9
|
10.15
|
|
Diseases of the eye and adnexa, diseases of the ear and mastoid process (C7 & C8)
|
H00–H02, H04–H05, H10–H11, H15–H18, H20–H21, H25–H26, H30–H31, H33–H35, H43–H47, H49–H57,
H60–H61, H69, H71–H74, H80–H81, H83–H93
|
9.95
|
|
Diseases of the skin and subcutaneous tissue (C12)
|
L03, L04, L20–L30, L45, L50, L52–L68, L70–L85, L90–L92, L98
|
9.81
|
|
Diseases of the digestive system (C11)
|
K00–K11, K14
|
9.77
|
|
All encephalopathy and cerebral oedema
|
G92, G93.1–G93.6
|
8.52
|
|
Certain infectious and parasitic diseases (C1)
|
A59–A60.0, A60.9, A63–A64, A71–A74, B07–B09, B35–B36, B74.4–B74.8, B75, B85–B88, B95–B97
|
7.84
|
|
Pneumonitis
|
J69
|
7.68
|
|
Diseases of the nervous system (C6)
|
G43–G44, G47–G52, G54, G56–G58
|
6.68
|
|
Diseases of the respiratory system (C10)
|
J30, J33, J34.2, J35
|
5.88
|
|
Congenital malformations, deformations and chromosomal abnormalities (C17)
|
Q16–Q18, Q36, Q54, Q65, Q67–Q68, Q72–Q74, Q82–Q83
|
3.33
|
|
Embolism and thrombosis
|
I74, I81
|
1.40
|
|
Cardiopaty complications and unspecified cardiac diseases
|
I51
|
0.73
|
*ICD 10: International Classification of diseases – Tenth revision
Finally, as considerable differences exist in the degree of completeness of the vital
registration among the Brazilian regions, the proportion of all deaths that is registered
for the population covered by the vital registration system has been estimated separately.
The “Rede Intergerencial de Informações para a Saúde” (RIPSA) coverage estimates between
1996 and 2011 were used to perform corrections of underreporting for both sexes[12], and estimated by sex. Underreporting correction was based on the ratio between
SIM death registers and “Instituto Brasileiro de Geografia e Estatística“(IBGE) death
estimates for the 1996-1999 period and the number of death estimated by active search
in 2000-2011[13]
,
[14].
Population data by age and sex were taken from the 1991, 2000 and 2010 Brazilian censuses[14]. Intercensuses population estimates by age and sex were obtained by logarithmic
interpolation of the censuses population.
In order to control the effect of age distribution variations in the period and among
regions, the mortality rates (per 100 thousand inhabitants) were standardized for
the Brazilian population in 2010 by sex and age using the direct method.[14]
To verify mortality trends during these 15 years, a linear regression model was fitted
to the data. To adjust for the presence of first order autocorrelation, the residuals
of the regression were modeled as a first order autoregressive process[15]. With that, it was possible to test if the mortality series have a significant increasing
or decreasing trend. A state space model was also fitted to the data, aiming the estimation
of annual trends at every point in time[15].
RESULTS
Between 1996 and 2011 it was observed a steady decrease of mortality rates for stroke
for both sexes, with differences in the magnitude of decline among the regions. Age-adjusted
mortality rates were higher among men for all regions. The South and Central West
regions had the smallest age-adjusted rates in 1996 and 2011. In 2011, there was an
important declining of age-adjusted mortality rates for both sexes, as well as a narrowing
of the range among the region rates. As expected, the mortality rates became higher
after correction and a higher impact of the correction can be observed among rates
from the North and Northeast regions, mainly in 1996. In 2011, smaller variations
of rates before and after correction can be noticed for all regions, but the higher
corrections remain restricted to the North and Northeast regions ([Table 2]).
Table 2
Stroke age-adjusted mortality rates before and after correction, among the Brazilian
regions, in 1996 and 2011.
|
Regions
|
Mortality rates (per 100,000 inhabitants)*
|
|
|
Men
|
Women
|
|
|
1996
|
2011
|
1996
|
2011
|
|
|
Pre
|
Post
|
Pre
|
Post
|
Pre
|
Post
|
Pre
|
Post
|
|
Central west
|
72.2
|
91.2
|
47.3
|
55.5
|
60.5
|
80.7
|
34.1
|
39.9
|
|
North
|
53.0
|
115.1
|
43.1
|
61.2
|
46.5
|
102.9
|
33.7
|
45.3
|
|
Northeast
|
53.2
|
124.3
|
49.0
|
64.0
|
42.6
|
107.8
|
36.9
|
47.8
|
|
South
|
89.6
|
98.2
|
49.0
|
55.6
|
63.9
|
69.5
|
32.6
|
36.7
|
|
Southeast
|
101.8
|
116.2
|
51.3
|
61.8
|
69.8
|
75.1
|
34.5
|
41.2
|
|
Brazil
|
82.9
|
113.6
|
49.6
|
60.9
|
58.2
|
84.4
|
34.7
|
42.3
|
*Before and after correction.
When rates are analyzed by age strata, it was observed an increment on mortality rates
by age in both sexes, as well as a consistent and impressive decline of these rates
in all age groups between 1996 and 2011 ([Table 3]).
Table 3
Age-specific mortality rates from stroke, by sex, in 1996 and 2011.
|
Age group (years)
|
Mortality rates (/100.000inhab)
|
|
|
Men
|
Women
|
|
|
1996
|
2011
|
1966
|
2011
|
|
30–34
|
13.9
|
6.6
|
11.7
|
5.1
|
|
35–39
|
25.6
|
12.3
|
21.9
|
10.4
|
|
40–44
|
46.5
|
22.4
|
39.4
|
20.1
|
|
45–49
|
82.1
|
38.5
|
68.2
|
33.6
|
|
50–54
|
122.2
|
65.9
|
97.1
|
48.5
|
|
55–59
|
212.1
|
110.8
|
149.8
|
71.1
|
|
60–64
|
308.9
|
172.3
|
210.3
|
108.7
|
|
65–69
|
498.6
|
289.6
|
352.4
|
184.2
|
|
Total
|
113.6
|
60.9
|
84.4
|
42.3
|
The decreasing trends among all Brazilian regions were statistically significant,
with higher values of decline in the Northeast and the North regions for both sexes
([Table 4]).
Table 4
Annual linear trend of stroke mortality rates among Brazilian regions, according to
the linear regression model with autoregressive errors, from 1996 to 2011.
|
Brazilian regions
|
Beta values*
|
|
|
Male
|
Female
|
|
Central West
|
-2.823
|
-2.829
|
|
North
|
-3.425
|
-3.358
|
|
Northeast
|
-4.010
|
-3.974
|
|
South
|
-3.082
|
-2.223
|
|
Southeast
|
-3.082
|
-2.262
|
*linear regression analysis, all p-values <0.001
Estimates of the annual trends in stroke mortality by sex show important declining
rates between 2000 and 2002, with smaller and steady values between 2006 and 2011
([Figure]). According to the state space model, trend evolution in all Brazilian regions show
a significant decrease in stroke mortality compared to the previous year. Among men,
the decrease was more pronounced between 2000 and 2002 in the North, Northeast and
Southeast Regions. In the South Region the decreasing occurred up to 2005 and in the
Midwest, after an initial increase, the trend has been decreasing since 1999. In women,
the decrease was accentuated in 1999 and 2000 in the North and Northeast. In the Southeast
and South regions there was a steady decrease until 2005, reaching intensity decreasing
from 2008. In the Midwest, the trend decreases sharply until 2002 and then stabilizes
([Figure]).
Figure Changes in stroke mortality rates among Brazilian regions according to space-state
regression model, from 1996 to 2011.* The rate of decreasing is relative to the previous
year
DISCUSSION
This study shows consistent declining trends of stroke mortality rates between 1996
and 2011. But before presenting these findings, a brief discussion of how to obtain
them is described. After all, methods do matter. When studying mortality trends for
the five regions of Brazil during 15 years, it is important to keep in mind that coverage
and quality of cause-of-death data varies across regions and time. Valid, reliable,
and comparable assessments of trends in causes of death from even the best systems
are limited by coverage and quality of data issues[16]. The first step of a mortality analysis consists in using traditional demographic
tools for correction of coverage. In this study, the number of deaths provided by
the SIM were corrected by taking into account the underreporting index estimated by
RIPSA and IBGE for each region and year. Without corrections for underreporting, developed
regions that generally have better coverage may seem to have higher mortality rates
than the poorest ones. Also, as coverage tends to improve over time, crude results
may show false increases on mortality rates in the future.
Besides differences in coverage, many deaths assigned to causes that cannot or should
not be considered underlying causes of death must be redistributed to a cause of death
that makes sense in terms of causality or public health interpretation[16]. Since the advent of the sixth revision, the ICD-10 has been used not only to code
deaths but also to cover all types of medical information, including non-fatal disorders
and nonspecific medical conditions[16]. In this study, causes such as atherosclerosis and hypertension, more plausible
as risk factors than underlying cause of death, were redistributed to cerebrovascular
and other cardiovascular diseases, according to preconized methods[1].
Quality of data information is a proxy of socioeconomic status of a region. The less
developed North and Northeast regions presented the higher proportion of correction
by coverage and by redistribution of causes of deaths. The decrease in the magnitude
of these corrections in 2011 may reflect improvements on information quality over
time and can contribute to narrowing the data quality gap between the northern and
southern regions of the country, these latter with data quality similar to developed
countries[17].
The North and Northeast regions also presented the higher mortality rates for both
sexes, although declining trends in mortality rates can be observed among all regions
of the country. The regression coefficient for the trend, presented on [Table 3], indicates around 3% annual decrease on mortality during these 15 years; and the
significance of this analysis indicates, with a 95% level of confidence, that this
declining trend really occurred. Higher declines of mortality rates in less developed
regions are generally predictable, since it is easy to have higher decreases where
the health indicators are worse.
Besides socioeconomic development, the significant decreasing in stroke mortality
rates may indicate the effect of cardiovascular risk factor control interventions,
as well as the huge increase (450%) on access to primary health services from 1981
to 2008[18]. These decreasing trends have been observed in Western nations since the 1970s and
have been attributed to improved control of hypertension. As observed in developed
countries, efforts towards diabetes mellitus and dyslipidemia control and smoking
cessation programs, particularly in combination with treatment of hypertension, may
have contributed to the decline in stroke mortality[19].
Although using different methodologies, our results are consistent with the majority
of published papers in the country [5]
,
[6]
,. The only dissonant note was the report of an increase in age-adjusted mortality
due to cerebrovascular accidents (ICD 10, I60-I69) from 2001 to 2006, maybe because
crude mortality data were not corrected [20].
But public health authorities cannot fool themselves by these good trends, as much
more effort still remains to be done. Besides having unequal distribution and being
a recent phenomenon in Brazil, the current mortality rates are still very high. Stroke
mortality has been falling rapidly in developed countries for more than 40 years[21]. The current burden of stroke mortality observed in the main Brazilian cities are
much higher than in the United States, Canada and western European countries, and
similar to what is observed in Eastern Europe and Japan. Compared to other Latin American
countries, Brazil also has the highest rates, for both sexes[22]. Even after the impressive decline among all age strata, the current mortality rates
observed in Brazilian adults and middle-aged are higher than mortality rates among
elderly from developed countries[2]
,
[3]. All over the world, in 2005, about 40% of stroke victims were less than 70 years
of age[23]. These results contradict the concept of stroke as a disease of the elderly and
reinforce the need for cardiovascular health promotion strategies based on the life-course
approach.
In order to establish preventive measures, it is important to differentiate the stroke
subtypes. Cerebral ischemia is associated to atherosclerosis and can be prevented
by policies aiming the reduction of cardiovascular risk factors. On the other hand,
hypertension is the primary cause of hemorrhagic stroke among those aged 40 or more
years (AHA/ASA Guidelines). Unfortunately, the Brazilian mortality data still lacks
specificity. From 2005 to 2007, the annual average of ill-defined codes for Brazilian
Capitals were very high: 31.8% of code I64.0 (stroke not specified as hemorrhagic
or ischemic), 25.2 % as code I61.9 (non-specified intracerebral hemorrhage) and 11.6%
as code I67.8 (other cerebrovascular diseases)[24]. A reappraisal of stroke mortality trends in Brazil between 1979 and 2009 showed
that mortality are declining in the country for all strokes subtypes, although these
estimates did not considered quality differences on registry, redistribution due to
garbage codes or ill-defined diseases[25].
The low access to neuroimaging diagnosis may partially explain the paucity of data
mortality on stroke subtypes. In São Paulo, the wealthiest State in Brazil, the changes
of stroke mortality rates between 1996 and 2003 revealed an annual reduction of all
types of stroke (-3.9%) and of stroke subtypes as intracerebral hemorrhage (-3.0%)
and cerebral infarction (-2.7%) as well as a decline of ill-defined stroke (-7.4%)
for men. The switch of ill-defined cases to stroke subtype categories due to a better
clinical diagnosis may have blurred a real decline of both cerebral infarction and
intracerebral hemorrhagic stroke among women[26].
The high proportion of ill-defined causes and the lack of stroke subtypes classification
of Brazilian death certificates are markers of low data quality, usually related to
the access or the quality of medical care received by the population[11]. Besides educational strategies and advocacy among doctors aiming the description
of stroke subtype on death certificates, it is essential to provide referral hospitals
with adequate diagnosis equipment, mainly in less developed regions. Although it have
been pointed out that there is no need to increase the number of machines for computed
tomography scans or magnetic resonance imaging in Brazil[27], the availability of these diagnosis tools seems to be uneven. A national analysis
of 16,879 hospital records from April 2006 to December 2007 showed that at least one
CT scan were performed in only 28.6% of the stroke admissions under the Brazilian
Unified National Health System. Moreover, 91.1% of these exams were performed in South
and Southeast regions[28].
The main strength of this study relies on the rigorous methodology and the use of
all modern techniques of analysis of mortality data. But our study is limited by the
lack of data of stroke incidence and case-fatality data for the country. The decline
in stroke mortality rates may reflect both reduced incidence or lower case-fatality
rates. Greater case-fatality rates could account for some of the increased mortality
in the poorest region of the country, since quality of care varies substantially among
these regions[28].
Moreover, it is important to analyze the burden of stroke as a non-fatal outcome.
After ten years from the first stroke, cumulative survival rates for all types of
stroke were 35% among Framingham Study participants[29]. But how these patients survive? A recent update on stroke statistics on United
States estimates that on average, every 40 seconds, someone has a stroke. At six months
after stroke, 35% had depressive symptoms, 30% were unable to ambulate without assistance,
and 26% were dependent in activities of daily living[30]. There are no estimates of the global burden of stroke in Brazil. Our country is
an emerging middle-income country and our social and health structures are still inadequate
to face the challenges of rehabilitation care for patients who survive to the acute
phase of stroke. It will be necessary renewed emphasis on treatment of acute events
as well as secondary and primary prevention through treatment and control of risk
factors.
In conclusion, although good news is always welcome, health authorities must maintain
and improve the efforts in the way to continue the declining trend of stroke in Brazil.
The main results of this study seem to reflect the time-dependent effects of socioeconomic
and health policies aiming the reduction of cardiovascular risk factors. Actions towards
improving data quality must be on agenda of the public health services. It is also
mandatory to discuss the best practices to treat acute stroke and decreases post-stroke
morbidity.
