The patient, a boy born on October 3, 2009, was the third child of healthy parents. He was breast-fed and healthy. At 2 weeks of age, he became irritable, started feeding poorly, and produced large volumes of watery feces with some blood. At 17 days of age, he was taken to the Vaasa Central Hospital (Vaasa, Finland) for medical care. Blood was collected in a One BacT/Alert pediatric blood culture bottle (bioMérieux, Marcy l’Etoile, France) and incubated in the BacT/Alert automated culturing system at the clinical microbiological laboratory in Vaasa. The blood culture showed a gram-negative rod, which was identified as E. coli. Results of a test for the O157 antigen were negative. Because the neonate was severely ill, he was referred to the University Hospital in Pirkanmaa Hospital district, and the s E. coli train isolated from his blood was forwarded to the Helsinki University Hospital Laboratory, where the invasive strain from fecal specimens of the neonate and all 4 asymptomatic family members—the mother (31 years of age), father (32 years), sister (3 years), and brother (2 years)—was confirmed by detection of Stx by using the Premier EHEC EIA-test (Meridian Bioscience, Inc., Cincinnati, OH, USA). All the STEC isolates were then sent to the Bacteriology Unit (BU) of the National Institute for Health and Welfare (THL, Helsinki, Finland) for verification and more accurate phenotyping and genotyping. Fecal sampling continued until 3 consecutive STEC-negative results were obtained.

Laboratory examination indicated that the neonate had elevated levels of C-reactive protein (261 g/L [reference <3 mg/L]) and serum creatinine (246 µmol/L [reference 10–56 μmol/L). Later laboratory investigations of the neonate indicated metabolic acidosis, hyponatremia (118 mmol/L [reference 137–145 mmol/L]), and hyperkalemia (8.9 mmol/L [reference 3.3–5.2 mmol/L]). In addition, ultrasound showed enlarged kidneys. The neonate was given intravenous fluids and ceftriaxone in response to presumed sepsis. On October 27, the neonate was referred to the Department of Pediatric Nephrology and Transplantation at the University Hospital for Children and Adolescents in Helsinki for peritoneal dialysis. At admission, the neonate had a history of bloody diarrhea, STEC sepsis, thrombocytopenia, hemolytic anemia (plasma concentrations of lactate hydrogenase and hemoglobin were elevated) with fragmented erythrocytes in peripheral blood and acute uremia. Thus, D+ HUS was diagnosed. A kidney biopsy was not performed.

The neonate had low blood pressure but was anuric and overhydrated. Thus, continuous veno-venous hemodiafiltration with the support of an adrenalin infusion was started. As soon as hemodynamic and clinical conditions improved and the neonate stayed anuric, continuous veno-venous hemodiafiltration was switched to hemodialysis treatment. Because of continuously high C-reactive protein values and signs of abscess in the left kidney, a left-sided nephrectomy was performed on October 28. Histologic investigation of the kidney showed large areas of kidney necrosis, foci of abscesses, and chronic inflammation. The glomeruli of the kidneys were totally destroyed, and no typical early changes of thrombotic microangiopathy changes in HUS were seen. Peritoneal dialysis was continued because of the end-stage kidney disease but was unsuccessful because of continuous problems with hernias (2 inguinal hernia operations) and left-side pleural fluid. Thus, hemodialysis was continued, and the child was discharged on January 19, 2010, in good condition. hemodialysis treatment was performed 3×/week until April 12, 2010, when peritoneal dialysis started again in the University Hospital in Helsinki. The child had regular follow up in the outpatient clinic every 1–2 weeks in the Vaasa Central Hospital and University Hospital and every 3 months in the ward in the Hospital for Children and Adolescents in Helsinki. His nutrition was evaluated at least 1×/month by a pediatric renal nutritionist. The child’s neurologic development was normal.

His father was a suitable donor, and a kidney transplantation was performed in April 2011. The operation and posttransplantation period went without complications. After the transplantation, triple immunosuppression (cyclosporine, azatioprine, and methylprednisolone) was used, and no acute rejection episodes occurred. At discharge, the glomerular filtration rate was 91 mL/min. Through the most recent follow-up, kidney function has been stable.

Biochemical identification of the STEC strains was conducted by using an API 20E test strip (bioMérieux, Marcy l’Etoile, France). The ability to ferment sorbitol was additionally investigated on sorbitol-McConkey agar. By using the agar diffusion method with Müller-Hinton agar, susceptibility was tested for the following 12 antimicrobial agents: ampicillin, chloramphenicol, streptomycin, sulfonamide, tetracycline, ciprofloxacin, trimethoprim, gentamicin, nalidixic acid, cefotaxime, mecillinam, and imipenem (10). The production of the Stx1 and Stx2 was investigated by using a reversed passive latex agglutination kit VTEC-RPLA (Oxoid, Basingstoke, UK). Because all 6 strains were O nontypeable by the antiserum available at BU/THL, they were sent to the Statens Serum Institute (Copenhagen, Denmark) for further serotyping. H-typing was performed at BU/THL. Strains that were not able to migrate through a Graigie tube with semisolid agar were defined as nonmotile (H^–) (11).

Sixteen-plex PCR was used to detect the genes uidA, pic, bfpB, invE, hlyA, elt, ent, escV, eaeA, ipaH, aggR, stx₁, stx₂, estIa, estIb, and astA by using the primers and PCR conditions as described (12). The following control strains were used: RH 4283 (E 2348/69 [(13]) for enteropathogenic E. coli, RH 4266 (ATCC 35401) for enterotoxigenic E. coli, RH 4270 (ATCC 43895) for STEC, RH 6647 (145–46–215, Statens Serum Institute) for enteroinvasive E. coli, IH 56822 (patient isolate [14]) for enteroaggregative E. coli, and RH 6715 (ATCC25922) for E. coli negative control.

Pulsed-field gel electrophoresis using XbaI as restriction enzyme was performed according to the PulseNet USA protocol for E. coli O157:H7 (15). The clonal similarity index of the isolates was calculated by using unweighted pair group method with arithmetic mean clustering with the BioNumerics software version 5.10 (Applied Maths, Kortrijk, Belgium).

For sequencing, the whole 1,470-bp fragment of the stx₁ gene (including the −10 and −35 promoter regions) from the 6 STEC strains, isolated from blood and fecal samples from the patient and fecal samples from his asymptomatic family members were amplified by using PCR primers as described (16). The PCR products were purified by using a MONTAGE centrifugal filter device kit (Millipore, Billerica, MA, USA). Approximately 10 ng of the PCR product was forwarded to the FIMM Technology Center sequencing laboratory (Helsinki, Finland) for sequencing by using the forward primer (5′-TCGCATGAGATCTGACC-3′) and the ABI3730xl sequencer (Applied Biosystems, Foster City, CA, USA). The sequences were analyzed by using the Bioedit program (www.mbio.ncsu.edu/BioEdit/BioEdit.html) and the homology searches by using the online National Center for Biotechnology Information GeneBlast tool (www.ncbi.nlm.nih.gov/BLAST/).