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Infectious Disease and Microbiology: Hemolytic–Uremic Syndrome (HUS)
Hemolytic–uremic syndrome (HUS) is a serious clinical condition characterized by a triad of acute renal failure, microangiopathic hemolytic anemia, and thrombocytopenia. It is most commonly associated with infection by Shiga toxin–producing bacteria, particularly Escherichia coli O157:H7 (EHEC). HUS primarily affects young children but can occur at any age and is a major cause of acute kidney injury in pediatric populations.
Epidemiologically, HUS is closely linked to infections caused by enterohemorrhagic E. coli, with an incidence of approximately 1–5 cases per 100,000 people annually in industrialized countries. The infection is more common in children under 5 years old and tends to peak during warmer months, particularly from June to September. Although many individuals infected with EHEC develop only mild gastrointestinal symptoms, about 8% of cases during outbreaks progress to HUS, especially in vulnerable populations such as young children and the elderly.
Transmission is primarily food-borne and is strongly associated with the consumption of undercooked ground beef, unpasteurized milk, contaminated water, and fresh produce such as apples or melons. Cattle serve as the main reservoir, often carrying the organism asymptomatically in their intestines. Infection can also spread through person-to-person contact, particularly in settings such as daycare centers and nursing homes. Proper food handling, cooking, and hygiene practices are essential preventive measures.
The pathophysiology of HUS involves the production of Shiga-like toxin by EHEC. This toxin damages endothelial cells, particularly in the kidneys, leading to inflammation, platelet activation, and formation of microthrombi in small blood vessels. These processes result in mechanical destruction of red blood cells (hemolysis), platelet consumption (thrombocytopenia), and reduced renal perfusion, ultimately causing acute kidney injury.
Clinically, infection typically begins with abdominal cramps and watery diarrhea, which progresses within 24 hours to bloody diarrhea in most patients. Nausea and vomiting are common, while fever is usually absent or mild. As HUS develops, signs such as decreased urine output (oliguria), pallor from anemia, and fatigue become evident. The drop in hematocrit and platelet count are early laboratory indicators of disease progression.
Diagnosis is based on clinical findings and laboratory confirmation. Stool cultures using special media are required to identify EHEC, as routine cultures may miss the organism. Laboratory findings in HUS include anemia with fragmented red blood cells (schistocytes), elevated lactate dehydrogenase (LDH), low haptoglobin, thrombocytopenia, and elevated creatinine levels indicating renal impairment. Urinalysis may show hematuria and proteinuria.
Management of HUS is primarily supportive. Antibiotics are generally not recommended in EHEC infections, as they may increase toxin release and worsen the condition. Similarly, antimotility agents should be avoided because they can enhance toxin absorption. Treatment focuses on maintaining fluid and electrolyte balance, managing renal failure with dialysis if necessary, and providing blood transfusions when indicated. In severe cases, plasmapheresis may be used.
The prognosis of HUS varies depending on severity and patient factors. Despite advances in supportive care, mortality rates range from 5% to 20%, with higher rates in older adults. Among survivors, long-term complications are common, including chronic kidney disease and hypertension, with many patients eventually requiring dialysis or kidney transplantation.
Complications of HUS include severe anemia, thrombocytopenia, electrolyte disturbances, rhabdomyolysis, and permanent renal damage. Additionally, EHEC infection itself may cause hemorrhagic colitis or, less commonly, conditions such as thrombotic thrombocytopenic purpura. Early recognition and supportive management are critical to improving outcomes.
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