Purpose To investigate the risk of infections in the first year of life in infants born to mothers with systemic lupus erythematosus (SLE) compared to infants born to general population comparators, and to examine the role of preterm birth as a mediator of the association.
Methods Liveborn singletons born to mothers with SLE and general population comparators were identified in the Medical Birth Register (MBR; 2006–2012), sampled from the Swedish Lupus Linkage (SLINK) cohort (1987–2012). SLE was defined by ≥2 International Classification of Diseases (ICD)-coded visits in the National Patient Register (NPR) and MBR, with ≥1 visit before pregnancy. Infections were defined as any ICD-coded visit listing an infection diagnosis in the in- and outpatient records of the NPR or dispensed antibiotic prescriptions in the Prescribed Drug Register. Hospitalized infections were defined as a primary ICD-coded hospitalization. Modified Poisson regression models estimated risk ratios and 95% confidence intervals (RR; 95% CI) of infant infection associated with maternal SLE adjusted for maternal age, first-trimester smoking, and calendar year. Causal mediation analysis estimated the percentage of the total effect explained by preterm birth (<37 weeks).
Results Of 441 SLE offspring, 17% had an infection diagnosis in the first three months of life compared to 12% of 4,485 non-SLE offspring, with a corresponding RR of 1.4 [95% CI 1.1–1.7] which was greater for infants born preterm (1.8 [95% CI 1.2–2.9]). Hospitalized infections occurred in 5% of SLE offspring and 3% of non-SLE offspring in the first three months (RR 2.1 [95% CI 1.3–3.3]), and in 9% of SLE offspring and 5% of non-SLE offspring in the first year (RR of 1.6 [95% CI 1.1–2.2]), regardless of being born preterm. Fifty-two percent of the total effect of maternal SLE on any infection in the first three months was mediated through preterm birth.
Conclusions When looking at the first three months, maternal SLE was associated with a nearly 40% higher risk of any infection and a two-fold higher risk of hospitalized infections. Preterm birth may explain half of the association between maternal SLE and any infection in the first three months of life.
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