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Hospital Discharges and Mortality Registries: 2 Complementary Databases for the Epidemiological Surveillance of Stroke
Hospital Discharges and Mortality Registries: 2 Complementary Databases for the Epidemiological Surveillance of Stroke Enrique Ramalle-Gomara, PhD,* Elena Ruiz, PhD,* Marta Serrano, MD,† nica Bartulos, MD,†‡ Marıa-Angeles Mo Gonz alez, RN,* and Belinda Matute, MDx
Background: Stroke is a public health concern and the availability of a stroke registry would provide valuable information. Administrative hospital data and mortality registries have been previously suggested as suitable sources of information. The aim of this study was to evaluate the utility of merging data from a hospital discharge database and the mortality registry (MR) to estimate the incidence of stroke in La Rioja, Spain. Methods: A cross-sectional study about events of stroke occurred in our region in 2009 was carried out. Patients were selected among those registered in the discharge hospital database and in the MR, using the International Classification of Diseases. The databases were merged to detect duplicated occurrences and to estimate the number of cases identified by each source. Characteristics of the study population were analyzed and crude- and age-adjusted incidence rates were assessed. Results: Using both databases, 1133 stroke events were detected, 153 (13.5%) representing coincident or recurrent cases. A total of 980 incident stroke cases were obtained, 150 provided by the MR (15.3%) and 830 by the hospital discharge database (84.7%). Incidence of stroke was similar in men than in women, the ischemic stroke being the major type. Most of the study population (66%) were older than 74 years. Crude incidence rate was 304.6 per 100,000, and ageadjusted rates were 171.1 per 100,000 (adjusted to the European population) and 107.9 per 100,000 (adjusted to the World population). Conclusions: Considering both the Minimum Basic Data Set and the MR as data sources appears advisable to build a stroke registry to evaluate the incidence and to perform epidemiological surveillance of stroke. Key Words: Stroke—mortality registries—hospital discharge—incidence rate—surveillance. Ó 2013 by National Stroke Association
Introduction Stroke represents one of the major health public problems, particularly in industrialized countries, although
From the *Department of Epidemiology, La Rioja Regional Authority, Logro~ no, Spain; †Department of Neurology, San Pedro Hospital, Logro~ no, Spain; ‡Complejo Asistencial Universitario de Burgos, Burgos, Spain; and xDepartment of Neurology, Los Manzanos Hospital, Lardero, Spain. Received March 7, 2013; revision received April 24, 2013; accepted April 29, 2013. Address correspondence to Enrique Ramalle-Gomara, PhD, Direcci on General de Salud P ublica y Consumo, Calle Vara de Rey 8, 1a Planta, 26071 Logro~ no (La Rioja), Spain. E-mail: eramalle@ larioja.org. 1052-3057/$ - see front matter Ó 2013 by National Stroke Association http://dx.doi.org/10.1016/j.jstrokecerebrovasdis.2013.04.039
incidence and mortality rates vary between them.1 Those differences may be because of variations in the access to prevention, intensive care, or environmental factors. In our country, cerebrovascular diseases are among the most frequent causes of hospitalization and death, especially affecting the elderly population.2 Stroke incidence rates in Spain fluctuate between 120 and 300 cases per 100,000 people/year.3,4 Because of the progressive aging of the population, these diseases will continue to be a health concern and the establishment of health service planning would be advisable. The availability of a stroke registry would allow researchers and policy makers to describe disease burden and to design appropriate health strategies.5 Hospital administrative data have often been suggested as valuable cost-effective tools for providing information about stroke burden.6-8 However, approximately 6%-17% of incident
Journal of Stroke and Cerebrovascular Diseases, Vol. 22, No. 8 (November), 2013: pp e441-e445
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stroke cases are not identified by hospital discharge diagnoses.9,10 Using other databases, such as mortality registries, has been reported to improve stroke case ascertainment.11,12 The objective of this study was to evaluate the convenience of merging data from a hospital discharge database and the mortality registry (MR) to estimate the incidence of stroke in La Rioja, Spain.
Materials and Methods To estimate the impact of stroke in the population of La Rioja in 2009, we carried out a cross-sectional study using data from 2 administrative databases, the Minimum Basic Data Set (MBDS) and the MR. The MBDS13 is a hospital database carried out at hospital discharge, which collects several data of the assistance processes from the 2 public hospitals of La Rioja, a region with a population of approximately 350,000 inhabitants. Those 2 public hospitals serve 99.5% of the population of La Rioja.14 In the region, there is only 1 small private hospital, which has 48 beds. The MBDS includes up to 13 diagnoses for each patient and admission, one of them codified as the major diagnosis and the others as secondary or other diagnoses by means of the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM). The MR collects data of deceased in La Rioja including the underlying cause of death and some other implicated causes, all of them codified with the International Classification of Diseases, Tenth Revision (ICD-10). To estimate the burden of stroke in the population, patients were selected from the MBDS when presented any of the ICD-9-CM codes 430-435 in the primary discharge diagnosis. This strategy was chosen in a previous study as the most accurate one based on its sensitivity, specificity, and positive predictive value. Deceased from the MR were selected when presented any of the ICD-10 codes I60-69 as underlying cause of death.15 The project was approved by an Ethical Review Board. The 2 databases were merged using the unique medical history number assigned to each patient in La Rioja. A coincident event was considered when the date of admission to the hospital was 28 days or less from the date of death in the MR, and both events had been classified as the same stroke type.16 Furthermore, to evaluate the population risk of having a stroke, only the first event of each person was considered and the others were classified as recurrent events.17 Characteristics of the population selected from the MBDS, from the MR, and by merging both databases were analyzed. The number of cases was measured per age, gender, and each major type of stroke. Crude incident rates (total and by sex) and incident rates adjusted by the direct method with the World and the European age standard population were calculated. For the adjustment process, age-specific rates were ob-
tained for 18 groups of age in 5-year intervals starting from 0 to 5 years up to 85 years or older. Age means were compared by the Student–Fisher t test.
Results Among the 27,988 hospital occurrences registered in the MBDS in 2009, only 891 presented any of the ICD-9CM codes 430-438 in the primary diagnosis. Among those 891 events, 61 (6.8%) were recurrent events in the studied period. Characteristics of the 830 patients from the MBDS with a first-ever stroke are shown by age, sex, and stroke type in Table 1. Among 2,892 deceased registered in the MR in 2009, 242 people died because of an underlying cause of death codified with any of the ICD-10 codes of stroke. Among those 242 stroke events, 54 (22.3%) matched with MBDS events representing coincident cases (death of the patient within 28 days of the hospital admission date because of that stroke event) and 38 (15.7%) were recurrent events because the patient was also registered in the MBDS because of another stroke event. Thus, the MR added 150 (15.3%) new patients to those detected by the MBDS. People with stroke from the MR are shown by age, sex, and stroke type in Table 1. Therefore, among the 1,133 total stroke events detected considering both databases, 153 (13.5%) constituted the same or recurrent events. The MR provided 150 (15.3%) new cases to the 830 (84.7%) patients detected by means of the MBDS, which means that 980 incident stroke cases were detected in our region by merging both databases (Fig 1). Characteristics of the study population are shown in Table 1. The number of men with stroke was similar to the number of women, ischemic stroke being the major type in both cases. Most of the study population (66%) were older than 74 years. The mean age in women was 79.9 and in men was 74.7 (P , .001). Crude- and age-adjusted incident rates obtained are shown in Table 2. Crude incidence rate was slightly higher in women (309.6 versus 299.7 per 100,000 persons), although age-adjusted rates were higher in men.
Discussion Administrative databases, such as the MBDS, have been suggested as valuable sources to assess the burden of stroke.6-8,18 Nevertheless, it would be advisable to consider other databases to detect patients with stroke who are not admitted in the hospital and, therefore, are not included in the hospital administrative databases. Other authors have reported that estimates of stroke incidence is more reliable when considering mortality registries beside discharge data,11,12 so we decided to evaluate the number of new events provided by the MR of La Rioja and patients with stroke appearing in the MBDS.
COMPLEMENTARY DATABASES FOR THE EPIDEMIOLOGICAL SURVEILLANCE OF STROKE
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Table 1. Characteristics of people with stroke in the different population samples analyzed in La Rioja, year 2009 Patient characteristics
MBDS, N (%)
MR, N (%)
MBDS 1 RM, N (%)*
Total cases Year ages ,25 25-34 35-44 45-54 55-64 65-74 75-84 $85 Gender Male Female Stroke classification TIA Ischemic stroke Hemorrhagic stroke Late effect or ill defined
830 (100)
242 (100)
980 (100)
1 (.1) 4 (.5) 12 (1.4) 39 (4.7) 71 (8.6) 187 (22.5) 331 (39.9) 185 (22.3)
1 (.4) 1 (.4) 2 (.8) 4 (1.7) 10 (4.1) 17 (7.0) 88 (36.4) 119 (49.2)
2 (.2) 4 (.4) 14 (1.4) 41 (4.2) 76 (7.8) 196 (20.0) 380 (38.8) 267 (27.2)
426 (51.3) 404 (48.7)
111 (45.9) 131 (54.1)
486 (49.6) 494 (50.4)
200 (24.1) 469 (56.5) 130 (15.7) 31 (3.7)
0 (0) 39 (16.1) 88 (36.4) 115 (47.5)
200 (20.4) 491 (50.1) 171 (17.4) 118 (12.1)
Abbreviations: MBDS, Minimum Basic Data Set; MR, mortality registry; TIA, transient ischemic attack. *Cases detected in both databases have only been counted once.
The MR provided 15.3% of the first-ever stroke events that could be detected by merging both databases. Previous studies reported that 6%-17% of incident stroke cases are not identified by hospital discharge diagnoses.9,10 Therefore, we also deem that improvement in stroke research is achieved by considering MR in addition to the MBDS database. On the other hand, the total number of cases identified with hospital data may decrease; thus, it would be advisable to use more than a single administrative data.8
Both databases used in this study were registered more than 20 years ago and are filled in following standardized procedures. For that reason, we suggest that results from our study could be extrapolated for other regions and nationally. Population suffering stroke in our region, detected by merging the MBDS and the MR, showed similar characteristics to population of other studies. Occurrence of stroke considerably rises at approximately 75 years.7,1719 Both men and women displayed very close rates,18-20
1000
54
Figure 1. Number of patients with stoke detected by means of the 2 sources. Abbreviations: MBDS, Minimum Basic Data Set; MR, mortality registry.
Number of patients with stroke
900
61
800
150
54
700 600 500 400
776
776
300 200
38 54
100
150
0 MBDS
MR
MBDS or MR
Source only MBDS
only MR
MBDS & MR
MBDS: Minimum Basic Data Set; MR:Mortality Registry
Recurrent MBDS
Recurrent MR vs MBDS
E. RAMALLE-GOMARA ET AL.
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Table 2. Incidence rates of stroke per 100,000 inhabitants in La Rioja, year 2009 Male Case number Crude rate (95% CI) Specific rate (95% CI) ,25 25-34 35-44 45-54 55-64 65-74 75-84 $85 Adjusted rate, to the European population (95% CI) Adjusted rate, to the World population (95% CI)
486 299.7 (273.3-326.1) 2.49 (.0-7.36) 7.16 (.0-17.08) 28.61 (8.78-48.43) 127.69 (81.99-173.38) 287.26 (207.63-366.88) 883.05 (718.78-1047.33) 1982.20 (1704.69-2259.71) 3238.87 (2562.15-3915.58) 206.0 (187.7-224.4) 131.0 (119.3-142.6)
Female 494 309.6 (282.4-337.0) 2.60 (.0-7.70) 8.09 (.0-19.31) 24.18 (4.83-43.52) 50.21 (20.54-79.88) 154.25 (94.96-213.54) 618.14 (486.73-749.55) 1378.38 (1179.21-1577.55) 3133.75 (2674.67-3592.84) 139.3 (127.0-151.5) 86.2 (78.6-93.8)
Total 980 304.6 (285.6-323.7) 2.54 (.0-6.07) 7.60 (.15-15.04) 26.52 (12.63-40.42) 90.30 (62.66-117.94) 221.82 (171.95-271.69) 744.65 (640.40-848.90) 1635.32 (1470.90-1799.75) 3167.64 (2787.68-3547.59) 171.1 (160.4-181.8) 107.9 (101.1-114.6)
Abbreviation: CI, confidence interval.
and ischemic stroke was the most frequent type,9,17,21 except in the MR where the hemorrhagic stroke rate was the highest one.22 Regarding recurrent and coincident strokes, in our work, they represented 13.5% (including both) of total cases during the study period, a figure similar to previous studies that reported recurrent rates of approximately 12%.9,18 In contrast, other authors obtained higher recurrent rates, ranging from 22% to 30%, which may be explained because of the study population or the differences in ICD-9-MC codes and number of diagnoses considered.17,21 The annual incidence rate of stroke, age-adjusted to the World population, observed in our region (107.9 per 100,000 persons) was similar to the averaged rate obtained among high-income countries in a previous study that reviewed all the available data from populationbased stroke incidence studies over the past 4 decades (94 per 100,000 persons).23 Nevertheless, that study reported notable variations between countries. Incidence rate obtained in our study was similar to those detected in other European countries such as France (58-92 per 100,000 persons), the United Kingdom (73-155 per 100,000 persons), Ireland (118 per 100,000 persons), Italy (82-116 per 100,000 persons), or Denmark (80-106 per 100,000 persons). In contrast, regarding other studies carried out in Spain, our incidence rate, age-adjusted to the European population (171.1 per 100,000 persons), differs from the age-adjusted incidence rate in other regions: Menorca (116.3 per 100,000 persons in men and 65.8 per 100,000 persons in women),5 Castilla y Le on (83 per 100,000 persons), Extremadura (54 per 100,000 persons), or Comunitat Valenciana (96 per 100,000 persons).4 Those variations between different countries or regions could be a consequence of the design of the study, especially the patient selection criteria, the geographical influence, or lifestyle factors.
Although crude stroke incidence rate was slightly higher in women, adjusted incidence rates became higher in men. This fact was because of the confounding effect of the age because women were older than men. Several authors previously suggested that stroke incidence rates are usually lesser in women than in men as a result of genetic factors, the positive effects of estrogen on the cerebral circulation, the lesser blood pressure values, or the lesser prevalence of peripheral artery disease.24 Our study had some limitations. First, we did not know the proportion of recurrent cases of patients with a history of stroke. In consequence, stroke incidence could be slightly overestimated. Second, data based on discharge diagnoses and mortality may be likely to underestimate the true rates of stroke by focusing on the more acute and severely symptomatic patients. However, provided that the proportion of acute stroke patients not admitted to a hospital is constant over the time,25 administrative databases remain a possible convenient and feasible tool to monitor trends of stroke. Finally, inter-regional variations in the coding of hospital discharge data may affect the results, limiting comparability. In conclusion, considering both MBDS and MR as data sources appears advisable to build a stroke registry to evaluate the incidence and to perform epidemiological surveillance of stroke.
References 1. Bejot Y, Benatru I, Rouaud O, et al. Epidemiology of stroke in Europe: geographic and environmental differences. J Neurol Sci 2007;262:85-88. 2. Marrugat J, Arboix A, Garcıa-Eroles L, et al. Estimaci on de la incidencia poblacional y la mortalidad de la enfermedad cerebrovascular establecida isquemica y hemorr agica en 2002. Rev Esp Cardiol 2007;60:573-580.
COMPLEMENTARY DATABASES FOR THE EPIDEMIOLOGICAL SURVEILLANCE OF STROKE 3. Dıaz-Guzman J, Egido-Herrero JA, Gabriel-S anchez R, et al. Incidencia de ictus en Espa~ na. Bases metodol ogicas del estudio Iberictus. Rev Neurol 2008;47:617-623. 4. Vega T, Zurriaga O, Ramos JM, et al. Stroke in Spain: epidemiologic incidence and patterns; a health sentinel network study. J Stroke Cerebrovasc Dis 2009;18:11-16. 5. Heuschmann PU, Di CA, Bejot Y, et al. Incidence of stroke in Europe at the beginning of the 21st century. Stroke 2009;40:1557-1563. 6. Derby CA, Lapane KL, Feldman HA, et al. Trends in validated cases of fatal and nonfatal stroke, stroke classification, and risk factors in southeastern New England, 1980 to 1991: data from the Pawtucket Heart Health Program. Stroke 2000;31:875-881. 7. Matıas-Guiu J. La investigaci on en epidemiologıa del ictus en Espa~ na. ¿Estudios de base poblacional o utilizaci on de aproximaciones a partir del CMBD? Rev Esp Cardiol 2007;60:563-564. 8. Moore DF, Lix LM, Yogendran MS, et al. Stroke surveillance in Manitoba, Canada: estimates from administrative databases. Chronic Dis Can 2008;29:22-30. 9. Ellekjaer H, Holmen J, Kruger O, et al. Identification of incident stroke in Norway: hospital discharge data compared with a population-based stroke register. Stroke 1999;30:56-60. 10. Piriyawat P, Smajsova M, Smith MA, et al. Comparison of active and passive surveillance for cerebrovascular disease: The Brain Attack Surveillance in Corpus Christi (BASIC) Project. Am J Epidemiol 2002;156:1062-1069. 11. Leppala JM, Virtamo J, Heinonen OP. Validation of stroke diagnosis in the National Hospital Discharge Register and the Register of Causes of Death in Finland. Eur J Epidemiol 1999;15:155-160. 12. Mahonen M, Salomaa V, Keskimaki I, et al. The feasibility of combining data from routine Hospital Discharge and Causes-of-Death Registers for epidemiological studies on stroke. Eur J Epidemiol 2000;16:815-817. 13. Rivero A. El conjunto mınimo b asico de datos en el SNS: inicios y desarrollo actual. Fuentes Estadısticas 2000; 49:18-19.
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14. Consejerıa de Salud y Servicios Sociales. II Plan de Salud La Rioja 2009-2013 [homepage on the Internet]. 2013. Available at: http://www riojasalud es/f/old/ ficheros/2_plan_salud_la_rioja_2009-2013 pdf. Accessed April 15, 2013. 15. Kunst AE, Amiri M, Janssen F. The decline in stroke mortality: exploration of future trends in 7 Western European countries. Stroke 2011;42:2126-2130. 16. Sarti C, Stegmayr B, Tolonen H, et al. Are changes in mortality from stroke caused by changes in stroke event rates or case fatality? Results from the WHO MONICA Project. Stroke 2003;34:1833-1840. 17. Spolaore P, Brocco S, Fedeli U, et al. Measuring accuracy of discharge diagnoses for a region-wide surveillance of hospitalized strokes. Stroke 2005;36:1031-1034. 18. Johansen HL, Wielgosz AT, Nguyen K, et al. Incidence, comorbidity, case fatality and readmission of hospitalized stroke patients in Canada. Can J Cardiol 2006;22:65-71. 19. Leibson CL, Naessens JM, Brown RD, et al. Accuracy of hospital discharge abstracts for identifying stroke. Stroke 1994;25:2348-2355. 20. Tirschwell DL, Longstreth WT Jr. Validating administrative data in stroke research. Stroke 2002;33:2465-2470. 21. Roumie CL, Mitchel E, Gideon PS, et al. Validation of ICD-9 codes with a high positive predictive value for incident strokes resulting in hospitalization using Medicaid health data. Pharmacoepidemiol Drug Safety 2008; 17:20-26. 22. Reker DM, Rosen AK, Hoenig H, et al. The hazards of stroke case selection using administrative data. Med Care 2002;40:96-104. 23. Feigin VL, Lawes CM, Bennett DA, et al. Worldwide stroke incidence and early case fatality reported in 56 population-based studies: a systematic review. Lancet Neurol 2009;8:355-369. 24. Appelros P, Stegmayr B, Terent A. Sex differences in stroke epidemiology: a systematic review. Stroke 2009; 40:1082-1090. 25. Reker DM, Hamilton BB, Duncan PW, et al. Stroke: who’s counting what? J Rehabil Res Dev 2001;38:281-289.
Background: Stroke is a public health concern and the availability of a stroke registry would provide valuable information. Administrative hospital data and mortality registries have been previously suggested as suitable sources of information. The aim of this study was to evaluate the utility of merging data from a hospital discharge database and the mortality registry (MR) to estimate the incidence of stroke in La Rioja, Spain. Methods: A cross-sectional study about events of stroke occurred in our region in 2009 was carried out. Patients were selected among those registered in the discharge hospital database and in the MR, using the International Classification of Diseases. The databases were merged to detect duplicated occurrences and to estimate the number of cases identified by each source. Characteristics of the study population were analyzed and crude- and age-adjusted incidence rates were assessed. Results: Using both databases, 1133 stroke events were detected, 153 (13.5%) representing coincident or recurrent cases. A total of 980 incident stroke cases were obtained, 150 provided by the MR (15.3%) and 830 by the hospital discharge database (84.7%). Incidence of stroke was similar in men than in women, the ischemic stroke being the major type. Most of the study population (66%) were older than 74 years. Crude incidence rate was 304.6 per 100,000, and ageadjusted rates were 171.1 per 100,000 (adjusted to the European population) and 107.9 per 100,000 (adjusted to the World population). Conclusions: Considering both the Minimum Basic Data Set and the MR as data sources appears advisable to build a stroke registry to evaluate the incidence and to perform epidemiological surveillance of stroke. Key Words: Stroke—mortality registries—hospital discharge—incidence rate—surveillance. Ó 2013 by National Stroke Association
Introduction Stroke represents one of the major health public problems, particularly in industrialized countries, although
From the *Department of Epidemiology, La Rioja Regional Authority, Logro~ no, Spain; †Department of Neurology, San Pedro Hospital, Logro~ no, Spain; ‡Complejo Asistencial Universitario de Burgos, Burgos, Spain; and xDepartment of Neurology, Los Manzanos Hospital, Lardero, Spain. Received March 7, 2013; revision received April 24, 2013; accepted April 29, 2013. Address correspondence to Enrique Ramalle-Gomara, PhD, Direcci on General de Salud P ublica y Consumo, Calle Vara de Rey 8, 1a Planta, 26071 Logro~ no (La Rioja), Spain. E-mail: eramalle@ larioja.org. 1052-3057/$ - see front matter Ó 2013 by National Stroke Association http://dx.doi.org/10.1016/j.jstrokecerebrovasdis.2013.04.039
incidence and mortality rates vary between them.1 Those differences may be because of variations in the access to prevention, intensive care, or environmental factors. In our country, cerebrovascular diseases are among the most frequent causes of hospitalization and death, especially affecting the elderly population.2 Stroke incidence rates in Spain fluctuate between 120 and 300 cases per 100,000 people/year.3,4 Because of the progressive aging of the population, these diseases will continue to be a health concern and the establishment of health service planning would be advisable. The availability of a stroke registry would allow researchers and policy makers to describe disease burden and to design appropriate health strategies.5 Hospital administrative data have often been suggested as valuable cost-effective tools for providing information about stroke burden.6-8 However, approximately 6%-17% of incident
Journal of Stroke and Cerebrovascular Diseases, Vol. 22, No. 8 (November), 2013: pp e441-e445
e441
E. RAMALLE-GOMARA ET AL.
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stroke cases are not identified by hospital discharge diagnoses.9,10 Using other databases, such as mortality registries, has been reported to improve stroke case ascertainment.11,12 The objective of this study was to evaluate the convenience of merging data from a hospital discharge database and the mortality registry (MR) to estimate the incidence of stroke in La Rioja, Spain.
Materials and Methods To estimate the impact of stroke in the population of La Rioja in 2009, we carried out a cross-sectional study using data from 2 administrative databases, the Minimum Basic Data Set (MBDS) and the MR. The MBDS13 is a hospital database carried out at hospital discharge, which collects several data of the assistance processes from the 2 public hospitals of La Rioja, a region with a population of approximately 350,000 inhabitants. Those 2 public hospitals serve 99.5% of the population of La Rioja.14 In the region, there is only 1 small private hospital, which has 48 beds. The MBDS includes up to 13 diagnoses for each patient and admission, one of them codified as the major diagnosis and the others as secondary or other diagnoses by means of the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM). The MR collects data of deceased in La Rioja including the underlying cause of death and some other implicated causes, all of them codified with the International Classification of Diseases, Tenth Revision (ICD-10). To estimate the burden of stroke in the population, patients were selected from the MBDS when presented any of the ICD-9-CM codes 430-435 in the primary discharge diagnosis. This strategy was chosen in a previous study as the most accurate one based on its sensitivity, specificity, and positive predictive value. Deceased from the MR were selected when presented any of the ICD-10 codes I60-69 as underlying cause of death.15 The project was approved by an Ethical Review Board. The 2 databases were merged using the unique medical history number assigned to each patient in La Rioja. A coincident event was considered when the date of admission to the hospital was 28 days or less from the date of death in the MR, and both events had been classified as the same stroke type.16 Furthermore, to evaluate the population risk of having a stroke, only the first event of each person was considered and the others were classified as recurrent events.17 Characteristics of the population selected from the MBDS, from the MR, and by merging both databases were analyzed. The number of cases was measured per age, gender, and each major type of stroke. Crude incident rates (total and by sex) and incident rates adjusted by the direct method with the World and the European age standard population were calculated. For the adjustment process, age-specific rates were ob-
tained for 18 groups of age in 5-year intervals starting from 0 to 5 years up to 85 years or older. Age means were compared by the Student–Fisher t test.
Results Among the 27,988 hospital occurrences registered in the MBDS in 2009, only 891 presented any of the ICD-9CM codes 430-438 in the primary diagnosis. Among those 891 events, 61 (6.8%) were recurrent events in the studied period. Characteristics of the 830 patients from the MBDS with a first-ever stroke are shown by age, sex, and stroke type in Table 1. Among 2,892 deceased registered in the MR in 2009, 242 people died because of an underlying cause of death codified with any of the ICD-10 codes of stroke. Among those 242 stroke events, 54 (22.3%) matched with MBDS events representing coincident cases (death of the patient within 28 days of the hospital admission date because of that stroke event) and 38 (15.7%) were recurrent events because the patient was also registered in the MBDS because of another stroke event. Thus, the MR added 150 (15.3%) new patients to those detected by the MBDS. People with stroke from the MR are shown by age, sex, and stroke type in Table 1. Therefore, among the 1,133 total stroke events detected considering both databases, 153 (13.5%) constituted the same or recurrent events. The MR provided 150 (15.3%) new cases to the 830 (84.7%) patients detected by means of the MBDS, which means that 980 incident stroke cases were detected in our region by merging both databases (Fig 1). Characteristics of the study population are shown in Table 1. The number of men with stroke was similar to the number of women, ischemic stroke being the major type in both cases. Most of the study population (66%) were older than 74 years. The mean age in women was 79.9 and in men was 74.7 (P , .001). Crude- and age-adjusted incident rates obtained are shown in Table 2. Crude incidence rate was slightly higher in women (309.6 versus 299.7 per 100,000 persons), although age-adjusted rates were higher in men.
Discussion Administrative databases, such as the MBDS, have been suggested as valuable sources to assess the burden of stroke.6-8,18 Nevertheless, it would be advisable to consider other databases to detect patients with stroke who are not admitted in the hospital and, therefore, are not included in the hospital administrative databases. Other authors have reported that estimates of stroke incidence is more reliable when considering mortality registries beside discharge data,11,12 so we decided to evaluate the number of new events provided by the MR of La Rioja and patients with stroke appearing in the MBDS.
COMPLEMENTARY DATABASES FOR THE EPIDEMIOLOGICAL SURVEILLANCE OF STROKE
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Table 1. Characteristics of people with stroke in the different population samples analyzed in La Rioja, year 2009 Patient characteristics
MBDS, N (%)
MR, N (%)
MBDS 1 RM, N (%)*
Total cases Year ages ,25 25-34 35-44 45-54 55-64 65-74 75-84 $85 Gender Male Female Stroke classification TIA Ischemic stroke Hemorrhagic stroke Late effect or ill defined
830 (100)
242 (100)
980 (100)
1 (.1) 4 (.5) 12 (1.4) 39 (4.7) 71 (8.6) 187 (22.5) 331 (39.9) 185 (22.3)
1 (.4) 1 (.4) 2 (.8) 4 (1.7) 10 (4.1) 17 (7.0) 88 (36.4) 119 (49.2)
2 (.2) 4 (.4) 14 (1.4) 41 (4.2) 76 (7.8) 196 (20.0) 380 (38.8) 267 (27.2)
426 (51.3) 404 (48.7)
111 (45.9) 131 (54.1)
486 (49.6) 494 (50.4)
200 (24.1) 469 (56.5) 130 (15.7) 31 (3.7)
0 (0) 39 (16.1) 88 (36.4) 115 (47.5)
200 (20.4) 491 (50.1) 171 (17.4) 118 (12.1)
Abbreviations: MBDS, Minimum Basic Data Set; MR, mortality registry; TIA, transient ischemic attack. *Cases detected in both databases have only been counted once.
The MR provided 15.3% of the first-ever stroke events that could be detected by merging both databases. Previous studies reported that 6%-17% of incident stroke cases are not identified by hospital discharge diagnoses.9,10 Therefore, we also deem that improvement in stroke research is achieved by considering MR in addition to the MBDS database. On the other hand, the total number of cases identified with hospital data may decrease; thus, it would be advisable to use more than a single administrative data.8
Both databases used in this study were registered more than 20 years ago and are filled in following standardized procedures. For that reason, we suggest that results from our study could be extrapolated for other regions and nationally. Population suffering stroke in our region, detected by merging the MBDS and the MR, showed similar characteristics to population of other studies. Occurrence of stroke considerably rises at approximately 75 years.7,1719 Both men and women displayed very close rates,18-20
1000
54
Figure 1. Number of patients with stoke detected by means of the 2 sources. Abbreviations: MBDS, Minimum Basic Data Set; MR, mortality registry.
Number of patients with stroke
900
61
800
150
54
700 600 500 400
776
776
300 200
38 54
100
150
0 MBDS
MR
MBDS or MR
Source only MBDS
only MR
MBDS & MR
MBDS: Minimum Basic Data Set; MR:Mortality Registry
Recurrent MBDS
Recurrent MR vs MBDS
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Table 2. Incidence rates of stroke per 100,000 inhabitants in La Rioja, year 2009 Male Case number Crude rate (95% CI) Specific rate (95% CI) ,25 25-34 35-44 45-54 55-64 65-74 75-84 $85 Adjusted rate, to the European population (95% CI) Adjusted rate, to the World population (95% CI)
486 299.7 (273.3-326.1) 2.49 (.0-7.36) 7.16 (.0-17.08) 28.61 (8.78-48.43) 127.69 (81.99-173.38) 287.26 (207.63-366.88) 883.05 (718.78-1047.33) 1982.20 (1704.69-2259.71) 3238.87 (2562.15-3915.58) 206.0 (187.7-224.4) 131.0 (119.3-142.6)
Female 494 309.6 (282.4-337.0) 2.60 (.0-7.70) 8.09 (.0-19.31) 24.18 (4.83-43.52) 50.21 (20.54-79.88) 154.25 (94.96-213.54) 618.14 (486.73-749.55) 1378.38 (1179.21-1577.55) 3133.75 (2674.67-3592.84) 139.3 (127.0-151.5) 86.2 (78.6-93.8)
Total 980 304.6 (285.6-323.7) 2.54 (.0-6.07) 7.60 (.15-15.04) 26.52 (12.63-40.42) 90.30 (62.66-117.94) 221.82 (171.95-271.69) 744.65 (640.40-848.90) 1635.32 (1470.90-1799.75) 3167.64 (2787.68-3547.59) 171.1 (160.4-181.8) 107.9 (101.1-114.6)
Abbreviation: CI, confidence interval.
and ischemic stroke was the most frequent type,9,17,21 except in the MR where the hemorrhagic stroke rate was the highest one.22 Regarding recurrent and coincident strokes, in our work, they represented 13.5% (including both) of total cases during the study period, a figure similar to previous studies that reported recurrent rates of approximately 12%.9,18 In contrast, other authors obtained higher recurrent rates, ranging from 22% to 30%, which may be explained because of the study population or the differences in ICD-9-MC codes and number of diagnoses considered.17,21 The annual incidence rate of stroke, age-adjusted to the World population, observed in our region (107.9 per 100,000 persons) was similar to the averaged rate obtained among high-income countries in a previous study that reviewed all the available data from populationbased stroke incidence studies over the past 4 decades (94 per 100,000 persons).23 Nevertheless, that study reported notable variations between countries. Incidence rate obtained in our study was similar to those detected in other European countries such as France (58-92 per 100,000 persons), the United Kingdom (73-155 per 100,000 persons), Ireland (118 per 100,000 persons), Italy (82-116 per 100,000 persons), or Denmark (80-106 per 100,000 persons). In contrast, regarding other studies carried out in Spain, our incidence rate, age-adjusted to the European population (171.1 per 100,000 persons), differs from the age-adjusted incidence rate in other regions: Menorca (116.3 per 100,000 persons in men and 65.8 per 100,000 persons in women),5 Castilla y Le on (83 per 100,000 persons), Extremadura (54 per 100,000 persons), or Comunitat Valenciana (96 per 100,000 persons).4 Those variations between different countries or regions could be a consequence of the design of the study, especially the patient selection criteria, the geographical influence, or lifestyle factors.
Although crude stroke incidence rate was slightly higher in women, adjusted incidence rates became higher in men. This fact was because of the confounding effect of the age because women were older than men. Several authors previously suggested that stroke incidence rates are usually lesser in women than in men as a result of genetic factors, the positive effects of estrogen on the cerebral circulation, the lesser blood pressure values, or the lesser prevalence of peripheral artery disease.24 Our study had some limitations. First, we did not know the proportion of recurrent cases of patients with a history of stroke. In consequence, stroke incidence could be slightly overestimated. Second, data based on discharge diagnoses and mortality may be likely to underestimate the true rates of stroke by focusing on the more acute and severely symptomatic patients. However, provided that the proportion of acute stroke patients not admitted to a hospital is constant over the time,25 administrative databases remain a possible convenient and feasible tool to monitor trends of stroke. Finally, inter-regional variations in the coding of hospital discharge data may affect the results, limiting comparability. In conclusion, considering both MBDS and MR as data sources appears advisable to build a stroke registry to evaluate the incidence and to perform epidemiological surveillance of stroke.
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