**Question:** An 8-year-old boy presents to casualty with history of diarrhoea, followed by decreased urine output. Blood examination shows thrombocytes 90,000/cm3. Diagnosis is

A. Hemolytic uremic syndrome
B. Leptospirosis
C. Viral infection
D. Plasmodium infection

**Correct Answer:**

**Core Concept:**

Hemolytic uremic syndrome (HUS) is a rare but severe complication of Shiga toxin-producing Escherichia coli (STEC) infection, which can lead to microangiopathic hemolytic anemia, thrombocytopenia, and acute kidney injury. The clinical presentation can mimic other conditions, such as viral infections, bacterial infections, or other autoimmune disorders.

**Why the Correct Answer is Right:**

In this case, the patient presents with symptoms of diarrhoea and decreased urine output, which can be seen in HUS. Additionally, a platelet count of 90,000/cm³ indicates thrombocytopenia, a hallmark feature of HUS. The patient's age (8 years old) also makes STEC infection more likely, as it typically affects older children and adults.

**Why Each Wrong Option is Incorrect:**

A. Hemolytic uremic syndrome (HUS) is not typically associated with diarrhoea and viral infections. Viral infections usually present with fever and respiratory symptoms, while diarrhoea is less common. Viral infections often cause gastroenteritis, which presents with abdominal pain, vomiting, and fever.

B. Leptospirosis is a zoonotic infection caused by Leptospira bacteria, which presents with fever, myalgia, and meningitis in addition to renal and liver involvement. It is less associated with thrombocytopenia and diarrhoea.

C. Viral infections are usually characterized by symptoms like fever, cough, and respiratory distress, with gastrointestinal symptoms being less common. Diarrhoea and decreased urine output are less common in viral infections and more likely in conditions like HUS.

D. Plasmodium infection is caused by malaria parasites and presents with fever, chills, and hepatosplenomegaly, rather than diarrhoea and decreased urine output. Additionally, malaria is more common in tropical regions, while the patient's age suggests a less likely cause.

**Clinical Pearls:**

1. In cases of diarrhoea and thrombocytopenia in a child, consider HUS as a potential diagnosis.
2. The patient's age and clinical presentation make viral infections less likely, as viral infections usually affect adults more frequently.
3. Diarrhoea and decreased urine output are less common in Plasmodium infections and are more typical in conditions like HUS.
4. Leptospirosis presents with fever, myalgia, and meningitis, with less common gastrointestinal symptoms compared to HUS.