The Brief Case: Cystoisospora belli in the duodenal aspirate of an HIV-infected child

A 10-year-old boy presented with a history of recurrent, large-volume, watery loose stools occurring multiple times a day, accompanied by progressive abdominal distension, intermittent low-grade fever, and significant unintentional weight loss for the past 2 years.The diarrheal episodes were non-bloody, and there was no history of passage of mucus, suggesting a non-inflammatory etiology.His appetite had gradually decreased, and his caregivers reported increasing fatigue and reduced activity levels.On physical examination, the child appeared pale and malnourished.Notably, oral candidiasis was present, along with generalized lymphadenopathy involving cervical and axillary nodes.Systemic examination did not reveal organomegaly, but signs of dehydration and pallor were evident.Laboratory investigations showed hypochromic microcytic anemia, with a hemoglobin level of 8.0 g/dL (reference range for age is 13.5 ± 2 g/dL), consistent with chronic illness and nutritional compromise.Five serial stool specimens collected on separate days were examined using direct wet mount, formalin-ether concentration, and modified acid-fast staining on both direct and concentrated specimens; all were unremarkable, with no parasitic forms detected.Given the chronic diarrhea and clinical suspicion of malabsorption, an upper gastrointestinal endoscopy with duodenal biopsy and aspirate examination was performed.Histopathological evaluation of the duodenal mucosa showed largely preserved villous architecture, with occasional mild villous flattening and non-specific inflammatory changes.No parasitic stages were identified.No special stains were performed on tissue sections, as routine histological examination did not reveal suspicious structures.Microscopic examination of the unstained duodenal aspirate revealed numerous elliptical oocysts morphologically consistent with Cystoisospora belli (Fig. 1A).Modi fied Kinyoun acid-fast staining was subsequently performed as a confirmatory test, demonstrating acid-fast elliptical oocysts characteristic of Cystoisospora species (Fig. 1B).Modified acid-fast staining is not routinely applied to duodenal aspirates unless parasitic structures are suspected on direct microscopy.Further evaluation for underlying immunosuppression revealed esophageal candidia sis on endoscopy, and human immunodeficiency virus (HIV) testing was positive by three ELISA kits, confirming underlying HIV infection contributing to his chronic presentation.Oral and esophageal candidiasis were considered supportive indicators of immunosup pression.His CD4 count was 150 cells/mm 3 .Based on these findings, a diagnosis of cystoisosporiasis in an HIV patient was established.He was started on antiretroviral therapy.The child was treated with 250 mg trimethoprim-sulfamethoxazole administered in two divided doses for 10 days.He showed notable symptomatic improvement, with reduction in stool frequency and gradual weight gain.