Background/Purpose: Infections are among the leading causes of hospitalization and mortality in patients with systemic lupus erythematosus (SLE); approximately 50% have a serious infection during their disease course. We investigated rates of serious infections requiring hospitalization according to immunosuppressant use in a nationwide cohort of SLE patients.  

Methods: We used the Medicaid Analytic eXtract (MAX) data system, with billing claims and demographic information for >24 million Medicaid enrollees from 47 states and Washington, DC, 2000-2006. We identified patients age 18-65 years with prevalent SLE (≥3 visits ≥30 days apart with ICD-9 codes of 710.0). We defined serious infections resulting in hospitalization using a method previously validated in an administrative database. We identified patients ever receiving immunosuppressants (IS; azathioprine, mycophenolate mofetil, cyclophosphamide, cyclosporine, tacrolimus), and corticosteroids (CS) and calculated incidence rates per 100,000 persons-years for bacterial (bacteremia, cellulitis, endocarditis, osteomyelitis, pneumonia, pyelonephritis, septic arthritis, listeriosis), fungal (pneumocystosis, candidiasis, cryptococcosis, aspergillosis, histoplasmosis) and viral (influenza, herpes zoster, cytomegalovirus) infections, occurring ≥7 days after receipt of the drug. We used Poisson regression to determine age, sex, and Medicaid enrollment duration-adjusted infection incidence rate ratios comparing SLE patients receiving no drugs to CS alone and IS and CS combined.

Results: We identified 43,351 patients with SLE. The mean age was 38 years (±12) and mean Medicaid enrollment duration was 3.3 person-years (±2.1). SLE patients were 98% female, 38% Black, 37% White, and 15% Hispanic. 18,659 (43%) patients received a CS alone and 13,913 (32%) received both a CS and an IS. During follow-up there were 13,986 serious bacterial infections: 23% bacteremia, 38% pneumonia and 24% cellulitis. There were also 47 cases of pneumocystosis, 382 cases of herpes zoster, and 114 cases of influenza all requiring hospitalization. The incidence rate for all infections was 1.2 times higher among those receiving a CS alone and combined with an IS, compared to those prescribed neither (Table). The incidence rate of viral infections was 2.4 times higher in patients receiving an IS and a CS combined and 1.3 times higher with a CS alone, compared to those prescribed neither.

Conclusion: In this large, diverse cohort, SLE patients receiving CS alone and both IS and CS combined had elevated incidence rates of serious infections requiring hospitalization, particularly viral infections. Further studies are needed to evaluate the causality of the observed associations accounting for patients’ baseline infection risk and drug-specific effects.

Table. Incidence Rates of Serious Infections by Subtype among Patients with SLE, 2000-2006*
	Total Infections		Bacterial Infections		Fungal Infections		Viral Infections
SLE Group	IR	IRR	IR	IRR	IR	IRR	IR	IRR
No IS or CS N=9197	102.05 (102.01-102.09)	1.0 (ref)	95.80 (95.76-95.84)	1.0 (ref)	3.65 (3.64-3.66)	1.0 (ref)	1.90 (1.90-1.91)	1.0 (ref)
CS Alone      N= 18659	120.73 (120.71-120.75)	1.20 (1.13-1.27)	112.42 (112.40-112.44)	1.19 (1.12- 1.26)	4.66 (4.65-4.66)	1.30 (1.19-1.41)	2.47 (2.47-2.54)	1.31 (1.20-1.43)
IS and CS N=13913	119.51 (119.48-119.53	1.19 (1.12-1.26)	109.06 (109.04-109.09)	1.16 (1.09-1.22)	5.10 (5.10-5.11)	1.35 (1.23-1.47)	4.62 (4.62-4.63)	2.39 (2.15-2.65)
*Crude incidence rates (IR) reported per 100,000 person-years with 95% CIs. Incidence rate ratios (IRR) with 95% CIs adjusted for age, sex and Medicaid enrollment duration.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/serious-infection-rates-among-patients-with-systemic-lupus-erythematosus-receiving-corticosteroids-and-immunosuppressants/