Causes of Hemolytic Uremic Syndrome
While the cause of HUS has not been established with certainty, researchers believe that an abnormal inflammatory reaction is stimulated in the blood stream causing platelets (the parts of the blood that form clots) to sludge in small blood vessels and form blood clots where they are not supposed to. This uses up the platelets and causes a shortage of them in the rest of the body. This abnormal reaction may be caused by a yet unidentified chemical that is produced in blood plasma (the fluid or non-cellular part of the bloodstream).

The triggering events for HUS are varied and include:

Enterohemorrhagic E. Coli is a type of bacteria that causes bloody diarrhea. E. coli is a very common type of bacteria in the body, and it is only the OH157:H7 type that causes the problem. It can be found in undercooked meat and other foods; and is one of the causes of food recalls and restaurant-related food poisoning outbreaks. This accounts for almost 90% of HUS in children. The 2011 outbreak of HUS in Germany was due to a different type of Shigela toxin-producing E. coli called 0104:H4.

Pregnancy and the early postpartum (after delivery) time period and the use of birth control pills are the more common associations with HUS.

Pneumonia caused by the Streptococcus pneumoniae bacteria is another possible precipitating factor. HUS is rare complication of this common infection. Most often, this pneumonia is treated with antibiotics as an outpatient. However, it is the cause of 40% of atypical HUS.

Medications may be also associated with HUS, including some chemotherapy and immunosuppression drugs, birth control pills, ticlopidine (Ticlid, an anti-platelet drug) and quinine (Quinerva, Quinite) an anti-platelet drug.
AIDS may be associated with HUS.