A Case of Resembling Hemolytic Uremic Syndrome Caused by Escherichia fergusonii in an Immunocompetent Adult

Escherichia fergusonii, a gram-negative rod and a member of the Enterobacteriaceae, was formerly known by the vernacular name enteric group 10 and further proposed as a new species by Farmer et al.1 in 1985. Within the genus Escherichia, E. fergusonii is the closest relative of E. coli, as shown by DNA hybridization (64% similarity).2 This makes it difficult to diagnose infections caused by these species, depending on the diagnostic method used.3 We report the case of a patient with a case resembling hemolytic–uremic syndrome (HUS) caused by E. fergusonii mimicking Shiga toxin-positive E. coli.

A 57-year-old man with fever (39.4℃) and myalgia for 2 days was admitted to our hospital. Three days earlier, he had undergone prostate biopsy at a primary urology clinic for urinary frequency; he had no other diseases. Laboratory results revealed the following: white blood cell count, 560/µL (normal: 4,800-10,800/µL); hemoglobin, 14.3 g/dL (normal: 13.0-18.0 g/dL); platelet count, 60,000/µL (normal: 130,000-400,000/µL); creatinine (Cr), 1.28 mg/dL (normal 0.70-1.20 mg/dL); and C-reactive protein, 22.19 mg/dL (normal: 0-0.5 mg/dL). A computed tomography scan of the abdomen/pelvis showed inflammation of the prostate gland without abscess, and urinalysis showed pyuria. Two hours later, he developed shock and immediately received intravenous meropenem and vancomycin, corticosteroid, and continuous infusion of an inotropic agent.

After 24 h of hospitalization, the patient recovered from hypotension. Following the detection of gram-negative bacilli in the patient’s blood and urine culture on day 2, the antibiotics were changed to meropenem and aztreonam. The hemoglobin levels (13.6 g/dL) remained unchanged from days 2 to 4; however, the platelet counts gradually dropped to 12,000/µL and Cr levels increased to 6.62 mg/dL on day 4.

On day 4, his blood and urine cultures revealed E. coli via the Vitek2 system (BioMérieux, Marcy l’Etoile, France) and matrix-assisted laser desorption–ionization-time of flight mass spectrometry (Brüker Daltonik, Bremen, Germany). Antibiotic susceptibility testing for the following antimicrobial agents revealed these minimum inhibitory concentrations (MICs): ciprofloxacin, MIC>2, resistant; ceftriaxone, MIC≤0.5 sensitive; and extended-spectrum beta-lactamase, negative. Owing to the exacerbation of renal failure, the patient received hemodialysis from day 6 to 10. Severe anemia was absent, but a peripheral blood smear revealed schistocytosis. His lactate dehydrogenase level was 587 U/L (reference range ≤250). Secondary HUS was suspected owing to marked thrombocytopenia, acute renal failure, and microangiopathic hemolytic anemia. We requested a microbiological test again for the cultured bacterium and Shiga toxin detection, suspecting E. coli O157: H7-related HUS. However, a quantitative polymerase chain reaction assay for Shiga toxin was negative, and as a result of 16S rRNA sequencing, E. fergusonii, not enterohemorrhagic E. coli, was confirmed as the causative pathogen. The patient recovered from thrombocytopenia, and acute renal failure did not progress even after stopping hemodialysis on day 11. His platelet count was within the normal range, and serum Cr recovered from 3.16 mg/dL at discharge to 1.57 mg/dL at day 19 after discharge.

So far, only a few cases of E. fergusonii bacteremia have been reported, and to the best of our knowledge, no previous study has reported this infection in an immunocompetent adult. Moreover, only one case of HUS caused by E. fergusonii has been reported in a 76-year-old elderly patient with a history of diabetes and stroke.4 HUS is a condition that affects the blood and blood vessels, and infection-related HUS is the most frequent form of HUS that occurs mainly following intestinal infection due to the Shiga toxin-producing E. coli. However, an atypical form of HUS due to an acquired or constitutional dysregulation of complement alternative pathway or secondary HUS due to coexisting diseases may also occur.5 Therefore, it is necessary to further study the techniques for accurate pathogen identification, and clinicians should consider HUS caused by E. fergusonii as well as E. coli and Shigella spp. even in immunocompetent adults.