Pediatric Hemolytic Uremic Syndrome in North-Eastern Germany During the STEC O45:H2 Outbreak in 2025: Clinical Features and Short-Term Outcomes.

BACKGROUND: Shiga toxin-producing Escherichia coli (STEC)-associated hemolytic uremic syndrome (HUS) is a leading cause of pediatric acute kidney injury. Between August and October 2025, Germany experienced an outbreak of the rare STEC serotype O45:H2, comprising 53 laboratory-confirmed pediatric HUS cases. Because O45:H2-associated HUS had previously been reported only sporadically, this study characterized its clinical course and compared it with HUS caused by non-O45:H2 STEC serotypes. METHODS: We retrospectively included all pediatric STEC-HUS cases treated in Northeastern Germany during the outbreak period. Microbiological confirmation was performed through cultivation and molecular typing at the National Reference and Consulting Laboratories. Patients were classified as O45:H2 or non-O45:H2 based on serotyping and the Robert Koch Institute (RKI) O45:H2 outbreak case definition. Clinical and laboratory parameters, dialysis requirements, transfusion needs, and short-term outcomes were compared. RESULTS: Thirty-seven children with STEC-associated HUS were included: 18 with O45:H2 and 19 with other serotypes. Patients with O45:H2 were significantly younger (median 2.0 vs 4.0 years, P = .01), while renal impairment at onset was comparable (minimal estimated glomerular filtration rate 8.0 vs 12 mL/min/1.73 m2). Dialysis was required in 65% of patients in both groups, with a trend toward longer duration in O45:H2 cases (median 10 vs 6 days). Hematologic parameters, markers of hemolysis, transfusion needs, neurological symptoms, and intensive care treatment were similar. One child died from myocardial failure. At 3-month follow-up, kidney function had recovered well in both groups. CONCLUSIONS: O45:H2-associated HUS was comparable in severity to non-O45:H2 STEC-HUS, while the younger age of affected children may indicate distinct host susceptibility or exposure patterns.