Design
Consecutive and standardised registry of new dementia cases in a delimited geographical area.
Geographical area of reference and population under surveillance
The Health Region of Girona (RSG) is located in the north-east of Catalonia (Spain). It has an extension of 5,517 km2, a population of 690,207 inhabitants (according to data from the Citizens Municipal Registry 2007) and a population density of 125.1 inhabitants/km2. The RSG includes 221 municipalities, 91 of which (43.5%) have 500 or less inhabitants, representing 4.3% of the population. Eighty per cent of the municipalities have 3,000 or less inhabitants and only eight municipalities have over 20,000 registered inhabitants. The RSG is composed of seven healthcare sectors that virtually coincide with the political-administrative division of the territory into 7 boroughs (Alt Empordà, Baix Empordà, Garrotxa, Gironès, Pla de l'Estany, Ripollès and Selva). The RSG provides 6 borough hospitals (healthcare level I) and a reference university hospital (healthcare levels I and II), with each hospital having an allocated reference population. Figure 1 shows the municipalities that make up the catchment area of each hospital and the number of inhabitants stratified into large groups. The ReDeGi keeps up a registry of new cases of dementia diagnosed in the 7 RSG hospitals.
Case registry
The ReDeGi fulfil the Centers for Disease Control (CDC) guidelines for evaluating a surveillance system [13]: it controls an assigned population under surveillance and provides standardised criteria for case definition and a simple and flexible system for data collection. The methodological principles and the functional structure of the ReDeGi have been previously described. [14, 15] In brief, the ReDeGi registers all new cases of dementia diagnosed in hospitals pertaining to the RSG, in accordance with the clinical diagnosis criteria established for dementia syndrome and the different subtypes according to the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR). [16] In a complementary fashion, clinical research criteria are used. [17–23] Diagnoses may have been made in the neurology or geriatrics outpatient consultation offices of each hospital. Case identification and notification to the ReDeGi is performed by the actual consultants of each RSG hospital that conducted the diagnostic process of dementia. A technician from the ReDeGi regularly visits the RSG hospitals and reviews the medical records of the dementia cases notified, writing the information in a 4-section data collection form: 1- identification of the centre (name of the hospital, date of admission and medical record number); 2- sociodemographics (date of birth, sex, nationality, place of residence, work position, schooling level, marital status, type of housing and healthcare referral device); 3- diagnosis characteristics (approximate date of the onset of symptoms, date of the diagnosis, DSM-IV-TR diagnostic criteria, additional diagnostic criteria for the subtype of dementia); 4- clinical data (score and date of administration of the Mini-Mental State Examination (MMSE) [24], score and date of administration of the Blessed Dementia Rating Scale (BDRS) [25], score of the Clinical Dementia Rating (CDR) [26], a past family history of dementia, present diagnosis of hypertension, diabetes mellitus, dislipidemia, stroke, thyroid disease and a past history of depressive disorder). The collected information is then entered into an electronic database that meets the confidentiality requirements for personal data protection in compliance with Spanish legislation.
Diagnosis of dementia
The validity of the diagnosis is based on the premise of validity of the diagnostic process on the part of the specialist physicians collaborating with the ReDeGi. Specialist physicians from each hospital (specialists in neurology or geriatrics) performed the registered diagnoses of dementia. Diagnosis was established on the basis of the medical history, an interview the patient and a close observer (family member or carer), a general medical examination, results from laboratory tests (haematology and basic biochemistry tests) and diagnostic neuroimaging (computerised axial tomography and/or brain magnetic resonance) when needed. The age of onset of symptoms was determined within the context of the interview with the informant during the diagnosis process. During this interview the specialist physician ask the informant about the approximate date of the onset of symptoms.
Statistical analysis
A descriptive analysis of the variables was carried out using central tendency and dispersion measures for quantitative variables and absolute and relative frequency measures for qualitative measures. The relative frequencies for the entered diagnoses of dementia were calculated and stratified by sex and the severity of the dementia. Bivariate statistical analysis was carried out to determine the existence of significant differences according to the sex and the severity of the dementia by applying parametric and non-parametric techniques, according to the distribution of data. [27]
To estimate the diagnostic coverage in the registry's catchment area, a dementia prevalence of 5.4% and an incidence of 8.8 cases were assumed per 1,000 people per year at risk for individuals aged 60 and over. These values were estimated by a group of international experts using a Delphi consensus. [28] Based on the available evidence from multiples epidemiological studies carried out all over the world, this report provides a consensus about the frequency indicators of dementia around the world. Specifically, the rates used in this study correspond to the geographic area known as EURO A, which includes Western European countries. Data for the population in the catchment are of the registry correspond to those published by the National Institute of Statistics for the referred area. [29] Results are expressed as absolute numbers and percentages, median (range) and mean (standard deviation) values, and 95% confidence intervals (CI). A statistical significance level of 95% was set for hypothesis contrasts.