Association between maternal systemic lupus erythematosus and infant infection: a population-based cohort study in Sweden

OBJECTIVES: The objectives of the study are to investigate infection risk in offspring born to women with systemic lupus erythematosus (SLE) compared with offspring born to women without SLE and examine the mediating role of preterm birth. DESIGN: This is a register-based cohort study. SETTING: Liveborn singletons born in Sweden, 2006-2021, were included in the study. PARTICIPANTS: 1248 infants born to mothers with SLE (≥2 International Classification of Diseases-coded visits in the National Patient Register (NPR) and Medical Birth Register, with ≥1 visit before pregnancy) and 34 886 infants born to women without SLE from the general population were included. PRIMARY AND SECONDARY OUTCOME MEASURES: The primary outcome was any visit for infection in the NPR or anti-infectives in the Prescribed Drug Register. The secondary outcome was hospitalised infection. Infection risks within 72 hours, within 1 month and within 1 year were estimated. RESULTS: SLE offspring had a higher risk of infection in the first 72 hours compared with non-SLE (2.1% vs 1.2%; risk ratios (RR) (95% CI) 1.62 (1.09 to 2.42)), the first month (5.2% vs 4.5%; RR 1.12 (0.88 to 1.43)) and first year of life (38.2% vs 37.2%; RR 1.09 (1.01 to 1.17)). The hospitalised infection risk for SLE offspring was similar to that of non-SLE (5.8% vs 5.5%, first year of life). The percentage of the total effect of maternal SLE on infant infection mediated through preterm birth was 86% for infection in the first 72 hours and 27% in the first year of life. CONCLUSIONS: The risk of infection in SLE offspring is most increased in the first 3 days after birth, and a proportion of this association can be explained by preterm birth. To prevent early neonatal infections, maternal SLE could be considered as a risk factor before allowing early discharge from postnatal care.