Hospitalisation for systemic lupus erythematosus associates with an increased risk of mortality in Australian patients from 1980 to 2014: A longitudinal, population-level, data linkage, cohort study

Abstract

Objective Mortality rates for patients with SLE have not been reported in Australia. This study determined the association between a hospitalisation for SLE with mortality. Methods Population-level cohort study of patients with SLE (n=2112; 25 710 person-years) and general population comparators (controls) (n=21, 120; 280 637 person-years) identified from hospital records contained within the WA Rheumatic Disease Epidemiological Registry from 1980 to 2013. SLE was identified by ICD-9-CM: 695.4, 710.0, ICD-10-AM: L93.0, M32.0. Controls were nearest matched (10:1) for age, sex, Aboriginality and temporality. Using longitudinal linked health data, we assessed the association between a hospitalisation for SLE mortality and mortality with univariate and multivariate Cox proportional hazards and competing risks regression models. Results At timezero, patients with SLE were similar in age (43.96 years), with higher representation of females (85.1% vs 83.4%, p=0.038), Aboriginal Australians (7.8% vs 6.0%) and smokers (20.5% vs 13.2%). Before study entry, patients with SLE (mean lookback 9 years) had higher comorbidity accrual (Charlson Comorbidity Index ≥1 item (42.0% vs 20.5%)), especially cardiovascular disease (CVD) (44.7% vs 21.0%) and nephritis (16.4% vs 0.5%), all p<0.001. During follow-up (mean 12.5 years), 548 (26.0%) patients with SLE and 2450 (11.6%) comparators died. A hospitalisation for SLE increased the unadjusted (HR 2.42, 95% CI 2.20 to 2.65) and multivariate-adjusted risk of mortality (aHR 2.03, 95% CI 1.84 to 2.23), which reduced from 1980 to 1999 (aHR 1.42) to 2000-2014 (aHR 1.27). Females (aHR 2.11), Aboriginal Australians (aHR 3.32), socioeconomically disadvantaged (aHR 2.49), and those <40 years old (aHR 7.46) were most vulnerable. At death, patients with SLE had a higher burden of infection (aHR 4.38), CVD (aHR 2.09) and renal disease (aHR 3.43), all p<0.001. Conclusions A hospitalisation for SLE associated with an increased risk of mortality over the 1980-2014 period compared with the general population. The risk was especially high in younger (<40 years old), socioeconomically disadvantaged and Aboriginal Australians.