Persistent Diarrhea Due to Cyclospora cayetanensis Diagnosed by Multiplex GI PCR in a Patient With HIV: A Case Report.

Cyclospora cayetanensisis a food- and waterborne coccidian parasite that causes prolonged watery diarrhea. Seasonal outbreaks and the potential for delayed diagnosis highlight the importance of recognizing this pathogen in patients presenting with persistent diarrhea. We present the case of a 49-year-old male with a history of HIV receiving bictegravir/emtricitabine/tenofovir alafenamide, type 2 diabetes mellitus, and hypertension who presented with three weeks of persistent watery diarrhea. He had previously been evaluated in the ED and discharged on ciprofloxacin and dicyclomine after a conventional bacterial stool culture did not identify an enteric pathogen, but his symptoms persisted. On repeat presentation, his vital signs were stable, and physical examination was unremarkable. A multiplex GI PCR panel detected C. cayetanensis. The patient received IV hydration and was discharged in stable condition with trimethoprim-sulfamethoxazole (TMP-SMX) 160/800 mg twice daily for 10 days. This case highlights the diagnostic delay that can occur when conventional bacterial stool culture is unrevealing and empiric antibiotic therapy fails to improve persistent diarrhea. Broader testing with multiplex GI PCR identified C. cayetanensis, allowing targeted therapy with TMP-SMX. The educational value lies in recognizing when to broaden diagnostic testing for a treatable parasitic infection after an inconclusive initial evaluation.