Bartonella-Associated Crescentic Glomerulonephritis (GN) and AKI: Infection Mimicking Autoimmunity

Introduction: Bartonella-associated GN is a rare, often misdiagnosed mimic of autoimmune RPGN. We present a case series of 7 marginally housed patients with AKI and biopsy-proven Bartonella-associated crescentic GN treated at a safety-net hospital in San Francisco between 2019–2024. The University of California San Francisco’s Institutional Review Board approved this study. Case Description: All patients presented with AKI, microscopic hematuria, new anemia, negative blood cultures, elevated ESR and CRP, hypocomplementemia (low C3 &/or C4) and biopsy-confirmed crescentic glomerulonephritis (6/7 had immune-complex GN, endocapillary and/or mesangial hypercellularity and deposits with IgG+, IgM ±, IgA+, C3+++, C1q++ staining; 1 had pauci-immune focal necrotizing GN). All patients were treated with pulsed-dose steroids prior to testing for Bartonella infection. Median age was 56 years (IQR 46.5-65) and 6/7 were male. Common features were marginalized housing status (shelter or incarcerated) (6/7) and months-long variable prodrome of fatigue, weight loss, rash or fever (6/7). Other risk factors were few, history of intravenous drug use (1/7), body lice (1/7) and cat exposure (2/7). None had diabetes or hypertension. Urinalyses showed hematuria (7/7), pyuria (6/7), and variable proteinuria (sub-nephrotic to nephrotic range). Only 1/7 had hepatitis-C infection; all tested negative for HIV, hepatitis B and RPR. All patients were positive for Bartonella quintana IgG (IgM +ve in 1) and Bartonella henselae IgG (all IgM -ve) with minimum dilution titers of 1:512 (positivity ≥1:256). All tested negative for ANCA antibodies, but 4 patients had PR3+ antigen, and 1 patient had PR3+/MPO+. Transesophageal echocardiography confirmed endocarditis in 3 patients, detected in 1, ruled it out in 2 and was not done in 1 patient. All patients were treated with doxycycline ± rifampin (or ceftriaxone) for a minimum 6-week course. Of the 7 patients, 3 had AKI-requiring dialysis; 2 died within 3 months, and 1 recovered renal function within 1 week; the 4 patients without AKI-D had persistent CKD stages 3-4 at follow up (3-36 months). Discussion: Early recognition of Bartonella-associated GN, which mimics autoimmune RPGN, and endocarditis evaluation are crucial to initiating appropriate treatment and improving outcomes. Marginalized housing is a major risk factor.