To examine the epidemiology of serious infections, a significant cause of morbidity and mortality in systemic lupus erythematosus (SLE), in a nationwide cohort of SLE and lupus nephritis (LN) patients.
Using the Medicaid Analytic eXtract database for the years 2000-2006, we identified patients ages 18-64 years who had SLE and the subset who had LN. We ascertained cases of serious hospitalized infections using validated algorithms, and we determined 30-day mortality rates. Poisson regression was used to calculate infection incidence rates and multivariable Cox proportional hazards models were used to calculate hazard ratios (HRs) for the first infection, adjusted for sociodemographic variables, medication use, and an SLE-specific risk adjustment index.
We identified 33,565 patients with SLE, 7,113 of whom had LN. There were 9,078 serious infections in 5,078 SLE patients and 3,494 infections in 1,825 LN patients. The infection incidence rate per 100 person-years was 10.8 in the SLE cohort and 23.9 in the LN subcohort. In adjusted models for the SLE cohort, we observed increased risks of infection in men as compared to women (HR 1.33 [95% confidence interval (95% CI) 1.20-1.47]), in blacks as compared to whites (HR 1.14 [95% CI 1.06-1.21]), and in users of glucocorticoids (HR 1.51 [95% CI 1.43-1.61]) and immunosuppressive drugs (HR 1.11 [95% CI 1.03-1.20]) as compared to never users. Hydroxychloroquine users had a reduced risk of infection as compared to never users (HR 0.73 [95% CI 0.68-0.77]). The 30-day mortality rate per 1,000 person-years among those hospitalized with infections was 21.4 in the SLE cohort and 38.6 in the LN subcohort.
In this diverse, nationwide cohort of SLE patients, we observed a substantial burden of serious infections with many subsequent deaths, particularly among those with LN.