Hemolytic uremic syndrome

Hemolytic uremic syndrome is a thrombotic microangiopathy defined by the simultaneous presence of microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. The syndrome exists in two principal forms: typical HUS, which follows infection with Shiga toxin-producing organisms, and atypical HUS (aHUS), which results from genetic mutations causing uncontrolled complement system activation. Both forms converge on a common pathway of endothelial damage, platelet activation, and widespread microvascular thrombosis.

The clinical course typically begins with gastrointestinal prodrome including bloody diarrhea, fever, vomiting, and abdominal cramps appearing 1 to 10 days after exposure, with median onset around 3-4 days. HUS itself manifests 5-10 days later, often as diarrhea begins to improve, characterized by declining platelet count, hemolytic anemia with schistocytes on peripheral smear, and deteriorating renal function including decreased urine output and hematuria. While children represent the majority of cases and most achieve full recovery, a subset develops severe complications including neurological impairment (seizures, confusion, cerebral convulsions), heart failure, and permanent renal damage. Adults, particularly the elderly, experience more complicated disease trajectories with higher mortality risk.

HUS occurs at an incidence of approximately 1.5 cases per 100,000 population annually, with typical HUS accounting for 90-95% of cases and atypical HUS representing the remaining 5-10%. The geographic distribution mirrors that of Shiga toxin-producing E. coli infection, with foodborne outbreaks linked to undercooked ground beef, contaminated produce, and unpasteurized dairy products representing primary exposure sources. Seasonal variation typically shows increased incidence during warmer months. Surveillance burden includes both sporadic case monitoring and outbreak investigation, with particular attention to identifying common source exposures in cluster detection.

Typical HUS transmission occurs through ingestion of Shiga toxin-producing E. coli, with O157:H7 representing the most frequently implicated serotype. Bacteria colonize the intestinal mucosa and produce Shiga toxins (Stx1, Stx2, or both), with Stx2-producing strains demonstrating greater virulence and higher HUS conversion rates. The toxins damage the intestinal endothelial barrier, gaining access to systemic circulation where they target renal glomerular endothelium. Secondary bacterial causes include Streptococcus pneumoniae, Shigella, and Salmonella species. Atypical HUS is not acquired through infection but rather results from inherited or acquired dysregulation of the complement alternative pathway.

Children under 5 years represent the highest-risk population for both STEC infection and subsequent HUS development, though most pediatric cases achieve complete recovery. The elderly population experiences disproportionately severe outcomes with higher rates of neurological complications, cardiac involvement, and mortality. Individuals with complement factor mutations (CFH, CFI, MCP, C3, Factor B) are susceptible to atypical HUS, which may present without preceding diarrheal illness and demonstrate relapsing patterns. Immunocompromised persons and those with underlying renal disease face elevated risk of adverse outcomes following typical HUS.

Primary prevention centers on food safety measures including thorough cooking of ground beef to internal temperatures sufficient to eliminate E. coli, avoidance of unpasteurized dairy products and juices, and rigorous hand hygiene following animal contact and bathroom use. The role of antibiotic prophylaxis in preventing HUS following confirmed STEC infection remains controversial; early studies suggested potential harm through enhanced toxin release, while more recent investigations indicate either neutral or potentially beneficial effects. Public health interventions emphasize rapid identification and recall of contaminated food products, with surveillance systems designed to detect outbreak clusters through laboratory-based pathogen identification and subtype characterization.

Surveillance for HUS operates at the intersection of infectious disease and renal registry monitoring, requiring integration of clinical case definitions with laboratory confirmation. The condition serves as a sentinel event for STEC infection, with HUS cases triggering retrospective food exposure history collection and potential outbreak investigation. Case definitions typically require the triad of anemia, thrombocytopenia, and acute kidney injury, with differentiation from thrombotic thrombocytopenic purpura (TTP) based on renal predominance and presence of preceding diarrhea. Atypical HUS cases warrant genetic counseling and family screening given the hereditary complement disorders. Temporal clustering of cases, particularly among children, should prompt immediate foodborne outbreak assessment.

1. 1 Wikidata. hemolytic-uremic syndrome.
2. 2 Wikipedia. Hemolytic–uremic syndrome - Wikipedia.

ICD-10

ICD-11

Total cases

593

Peak month

2019-12

Coverage

1 reporting countries · 2019-02-02 → 2026-05-09