Influenza A(H1N1) triggered atypical hemolytic uremic syndrome in a child with homozygous CD46 variant successfully treated with ravulizumab: a case report.

To describe a pediatric case of aHUS triggered by influenza A(H1N1) infection in a patient with a homozygous pathogenic variant in CD46, successfully treated with ravulizumab. A previously healthy 12-year-old girl presented with a four-day history of fever, diarrhea, abdominal pain, mucosal bleeding, jaundice, and acute kidney injury. Initial evaluation confirmed microangiopathic hemolytic anemia and thrombocytopenia. ADAMTS13 activity was preserved. Nasopharyngeal polymerase chain reaction testing detected influenza A virus subtype H1N1, and a multiplex gastrointestinal polymerase chain reaction panel identified enteropathogenic Escherichia coli; Shiga toxin was not detected. Despite therapeutic plasma exchange and hemodialysis, there was no hematologic or renal improvement, and multi-organ involvement persisted, including respiratory failure and elevated pancreatic enzyme levels. Terminal complement inhibition with ravulizumab was initiated, leading to rapid hematologic normalization and full renal recovery by day 106. Genetic testing revealed a homozygous splice-site variant in CD46 (c.286 + 1G > C), consistent with atypical hemolytic uremic syndrome. This case underscores the importance of early C5 inhibition in complement-mediated thrombotic microangiopathy associated with defects in membrane-bound complement regulators, in which therapeutic plasma exchange may have limited efficacy. It also highlights how infections can act as triggers that unmask underlying genetic susceptibility.