Scottish Index of Multiple Deprivation (SIMD) indicators as predictors of mortality among patients hospitalised with COVID-19 disease in the Lothian Region, Scotland during the first wave: a cohort study

Abstract

Background: Sars-CoV-2, the causative agent of COVID-19, has led to more than 226,000 deaths in the UK and multiple risk factors for mortality including age, sex and deprivation have been identified. This study aimed to identify which individual indicators of the Scottish Index of Multiple Deprivation (SIMD), an area-based deprivation index, were predictive of mortality.

Methods: This was a prospective cohort study of anonymised electronic health records of 710 consecutive patients hospitalised with Covid-19 disease between March and June 2020 in the Lothian Region of Southeast Scotland. Data sources included automatically extracted data from national electronic platforms and manually extracted data from individual admission records. Exposure variables of interest were SIMD quintiles and 12 indicators of deprivation deemed clinically relevant selected from the SIMD. Our primary outcome was mortality. Age and sex adjusted univariable and multivariable analyses were used to determine measures of association between exposures of interest and the primary outcome.

Results: After adjusting for age and sex, we found an increased risk of mortality in the more deprived SIMD quintiles 1 and 3 (OR 1.75, CI 0.99-3.08, p = 0.053 and OR 2.17, CI 1.22-3.86, p = 0.009, respectively), but this association was not upheld in our multivariable model containing age, sex, Performance Status and clinical parameters of severity at admission. Of the 12 pre-selected indicators of deprivation, two were associated with greater mortality in our multivariable analysis: income deprivation rate categorised by quartile (Q4 (most deprived): 2.11 (1.20-3.77) p = 0.011)) and greater than expected hospitalisations due to alcohol per SIMD data zone (1.96 (1.28-3.00) p = 0.002)).

Conclusions: SIMD as an aggregate measure of deprivation was not predictive of mortality in our cohort when other exposure measures were accounted for. However, we identified a two-fold increased risk of mortality in patients residing in areas with greater income-deprivation and/or number of hospitalisations due to alcohol. In areas where aggregate measures fail to capture pockets of deprivation, exploring the impact of specific SIMD indicators may be helpful in targeting resources to residents at risk of poorer outcomes from Covid-19.

Keywords: Covid-19; Deprivation; Mortality; SIMD indicators.

Fig. 1

Step-by-step representation of statistical analyses employed in the study. Legend: *Demographic and Clinical Parameters determined from Mutch et al. 2022 [5] “Performance status: A key factor in predicting mortality in the first wave of COVID-19 in South-East Scotland”. Demographic parameters = Age (in years), sex; Clinical parameters = Performance Status (WHO Standardized Categories); Admission pulse rate (in beats/minute); Haemoglobin concentration (in grams/Litre); Neutrophil count (cells × 10⁵); Lymphocyte count (cells × 10⁵); Creatinine (in milligrams/decilitre). SIMD score = quintile distribution; 12 relevant SIMD indicators = Income Deprivation Rate; Employment Deprivation Rate; Comparative Illness Factor; Hospital stays related to alcohol use; Hospital stays related to drug use; Standardised Mortality Ratio; Proportion of population prescribed drugs for anxiety, depression, and/or psychosis; Emergency stays in hospital; Proportion of working age population with no higher qualifications; Drive to GP (in minutes); Public Transport to GP (in minutes); Overcrowding rate (Scottish Index of Multiple Deprivation (2020, version 2)). ** Variables had P < 0.157 in the univariable analysis. P < 0.157 selected as a screening value appropriate for subsequent multivariable model selection by Akaike Information Criterion (AIC) with a study population of 710. (Timo and Ilkka 1986; Perez-Guzman et al. 2021)

Fig. 2

Cramer’s V Correlation Matrix of 12 selected indicators of deprivation plus age and sex. Deeper shading indicates higher degree of association. Legend: 1. Distance to nearest GP surgery per datazone, in minutes; 2. Distance to nearest GP surgery by public transport per datazone, in minutes; 3. Overcrowding rate; 4. Hospitalisations due to alcohol per datazone; 5. Hospitalisations due to drug use per datazone; 6. Emergency hospitalisations per datazone; 7. Employment rate; 8. Comparative Illness factor; 9. Income rate; 10. 16–19 year-olds without qualifications; 11. Standardised Mortality Ratio; 12. Prescriptions for anxiety, depression or psychosis per datazone; 13. Sex; 14. Age

Fig. 3

Forest Plots describing multivariable analyses of 3 SIMD indicators associated with increased mortality. Forest plots of odds ratios and 95% confidence intervals from three nested multivariable regression models investigating the association between mortality and: SIMD quintile (model 1); Income deprivation rate by quartile (model 2); Hospital stays due to alcohol use per datazone (model 3). Models were compared for goodness of fit based on Akaike Information Criterion (AIC): SIMD quintile (model 1, AIC: 692.06), income deprivation rate by quartile (model 2, AIC: 685.83), and hospital stays due to alcohol use per datazone (model 3, AIC: 679.59). Each multivariable model also contained: Age (in years), Sex, Performance Status (WHO Standardized Categories), Admission Pulse (beats/minute), Haemoglobin concentration (grams/Litre), Neutrophil count (cells × 10⁵), Lymphocyte count (cells × 10⁵), Creatinine (milligrams/decilitre). These variables were identified at the time of admission as risk variables in a companion paper (Mutch et al. 2022) [5]

Fig. 4

Violin plots. a The shape of the distribution of SIMD rank, in Lothian compared to Scotland. SIMD rank of 1 is most deprived and 6976 is least deprived. b The shape of the distribution of Income deprivation rate in Lothian compared to Scotland. c The shape of the distribution of datazones according to number of hospitalisations related to alcohol; this is a standardised ratio where 100 (dotted line) represents the expected number