Objective To investigate the rate of serious infections (SI) in systemic lupus erythematosus (SLE) compared to the general population.
Methods Individuals with incident SLE were identified from the Swedish National Patient Register (NPR) if they had two or more visits listing an SLE ICD code, at least one of which with a specialist, the first visit occurring Jan 2006 through Dec 2013. A non-SLE comparator group living in Sweden at the time the SLE case was diagnosed was matched on age, sex and county. We defined SI as a hospitalisation listing infection as main diagnosis from the NPR. Rates of SI per 1000 person-years (py) were calculated and age- and sex-adjusted Cox models were used to estimate hazard ratios and 95% confidence intervals (HR, 95% CI) comparing SLE to non-SLE. Because individuals can experience more than one SI, we also calculated the rate of infection by year since SLE diagnosis including multiple infections.
Results We identified 2846 individuals with SLE and 13 696 general population comparators. The average age at start of follow-up was 49% and 85% were female. Compared to the general population, individuals with SLE were more likely to have had a history of SI within a year before their first SLE visit (7.8% vs 0.8%). The incidence rate for SI in SLE was 51/1000 py, 26% of SIs were pneumonia and 1% were opportunistic infections. The HR for SI was 5.4 (95% CI: 4.8 to 6.2) comparing SLE to non-SLE. Six percent of the SLE group experienced more than one SI over the study period. The rate of SI allowing for multiple events was 92/1000 py which varied over time since diagnosis (figure 1).
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