The major cause of HUS in childhood is gastrointestinal infection with verocytotoxin (Shiga-like toxin)-producing bacteria, usually enterohemorrhagic Escherichia coli (VTEC/STEC), and in some tropical regions Shigella dysenteriae type I.Verocytotoxin-producing citrobacter freundii has also been reported. Within STEC infections, risk is determined more precisely by Shiga toxin genotype than by serogroup alone; STEC that produce Shiga toxin 2 are high-risk pathogens. E. coli O157 remains the best-characterized high-risk STEC, but clinically important non-O157 STEC also occur. In America and the UK, most cases are associated with E. coli serotype O157:H7, while other serotypes such as O26, O111, O103, and O145 are increasingly reported in Europe and elsewhere.

VTEC strains produce various toxins, the major ones being verocytotoxin-1 (Stx1) and verocytotoxin-2 (Stx2). Verocytotoxin-1 differs by one amino acid from Shiga toxin produced by Shigella dysenteriae type 1. Verocytotoxin-2 has multiple variants that are closely related to each other but have 55–60% homology to verocytotoxin1. HUS is mostly caused by verocytotoxin-2-producing strains.HUS can occur in the course of systemic diseases or physiopathological conditions such as pregnancy, after transplantation or after drug assumption.

Among other infectious causes, Streptococcus pneumoniae and influenza virus are notable non-STEC triggers of HUS.

Common causes of HUS may include:^[1][2][3][4]

• E. coli (70%)- Shiga-Toxin producing E.Coli (STEC)
  • Primary source of infection is usually undercooked or raw ground meat products, raw milk, or fecal contamination of vegetables
  • Other sources include swimming pools or lakes contaminated with feces
  • Usually cause self-limiting infection but can lead to HUS in some, particularly in young children and elderly
  • STEC is heat sensitive and destroyed by thorough cooking and WHO recommended guidelines for safer food should be used to prevent infections with foodborne organisms like STEC^[5].
• Other Shiga-Toxin bacteria like Shigella dysenteriae type-1. Among other infectious causes, Streptococcus pneumoniae and influenza virus are notable non-STEC triggers of HUS.^[6]

Less common causes of HUS include ^{[7][8][9][10]}

• Genetic mutations of complement genes/ complement factor abnormalities
• Infection with Campylobacter Jejuni or Salmonella Typhi
• Pneumococcal infection (commonly pneumonia, empyema, meningitis, and less commonly pericarditis, peritonitis, otitis media and bacteremia
• Pregnancy
• Autoimmune disease such as SLE, Antiphospholipid Syndrome
• Drug associated
  • Antineoplastic, immunosuppressive and anti platelet
• Organ Transplantation
• Human immunodeficiency viral infection such as HIV/AIDS

List the causes of the disease in alphabetical order: