A 40-year-old woman was diagnosed with SLE at 20 years of age. Her symptoms included a typical rash, severe multiple organ failure, consciousness disturbance and retinal vasculitis. A laboratory analysis revealed reduced C3, C4 and CH50 levels (20 mg/dL, 7 mg/dL and 10 U/mL, respectively) and anti-nuclear antibody positivity (640x, homogenous, speckled), and anti-DNA antibody negativity. She was in a severe condition and was refractory to the initial treatment of prednisolone (1 mg/kg/day). Plasmapheresis, high-dose methylprednisolone (1 g bolus for 3 days) and an increased dose of prednisolone (1.3 mg/kg/day) were necessary to achieve remission from SLE. After the initial therapy, her condition remained stable with the administration of prednisolone (10 mg/day) for more than 10 years. A regular blood examination showed a gradual increase in the patient's C-reactive protein (CRP) level from 3 months before her admission, which had previously been normal. At first, an exacerbation of SLE was suspected and the amount of prednisolone was increased to 15 mg/day. One month before the admission, she suffered from a high grade fever (39C) at night with shivering, chills and mild nausea. She was admitted to our hospital to undergo further examination. Her consciousness was clear, without diarrhea, cellulitis or arthritis. On admission, a complete blood cell count revealed anemia (Hb, 7.3 g/dL) with an increase in the number of fragmented red blood cells, leukocytosis (WBC, 18,880 /muL) with neutrophilia (93.5%), and severe thrombocytopenia (platelet count, 37,000 /muL). The patient's CRP level was elevated (14.95 mg/dL). Tests for anti-nuclear antibodies and anti-DNA antibodies were negative and the patient's complement values were normal (C3, 87 mg/dL, C4, 24 mg/dL, and CH50, 51 U/mL). An interferon-gamma release assay TB was negative and no vegetation was observed by transthoracic echocardiography. Computed tomography showed significant thickening of the patient's gallbladder wall (Fig. 1) and the values of alkaline phosphatase and gamma-glutamyltranspeptidase were also elevated; however, she had no abdominal pain. After admission, her high fever lasted and her anemia and thrombocytopenia advanced rapidly. The patient's blood cultures being negative, and the focus of infection had not been detected on the fourth day of admission. We were therefore forced to start methylprednisolone (1,000 mg/day) due to suspected acalculous cholecystitis which was thought to have occurred due to a flare of SLE or a complication of vasculitis. The next day, the patient's blood cultures were found to be positive (after 5 days of incubation) and microscopy showed gram-negative spiral bacteria (Fig. 2). The isolate was finally identified as H. cinaedi by a PCR and 16S rRNA gene sequencing. We considered that the patient's thrombocytopenia had been caused by H. cinaedi bacteremia, and stopped the bolus administration of methylprednisolone; prednisolone was reduced to the maintenance dose. With the administration of meropenem, the patient's temperature decreased and there was an improvement in her laboratory data with regard to her platelet count, CRP level, and the number of fragmented red blood cells. The clinical course is shown in Fig. 3. The antibiotic was changed and de-escalated to ampicillin, which caused a systemic drug eruption. Doripenem was administered for 3 weeks; thus, the total duration of treatment reached 5 weeks, at which point, the antibiotics were stopped due to pancytopenia. One month after the treatment, the H. cinaedi bacteremia relapsed with a high-grade fever and cellulitis (Fig. 4). Meropenem was administered intravenously for another 2 weeks, and 6 weeks of oral minocycline were given, no relapse occurred after this treatment.