Chronic Cystoisospora belli infection in an immunocompetent Myanmar refugee – microscopy is not sensitive enough

BACKGROUND: Cystoisosporiasis is an opportunistic infection seen more commonly in patients with acquired immunodeficiency syndrome. Although uncommon, Cystoisospora infection can occur in immunocompetent individuals but tend to be benign and self-limiting. Chronic infection however, has been described but diagnosis can often be challenging and requires a high clinical index of suspicion. CASE PRESENTATION: We present a case of delayed diagnosis of Cystoisospora belli (C. belli) in an immunocompetent 28-year-old refugee from Myanmar. She had a history of chronic diarrhea where exhaustive investigations over many years failed to reveal a diagnosis. Cystoisospora belli cysts were finally detected in stool 4 years after investigation commenced, and PCR testing on stored colon biopsies amplified a molecular product with 99 % sequence homology to C. belli. The patient improved promptly with trimethoprim-sulfamethoxazole treatment. CONCLUSION: In the appropriate clinical context we suggest molecular testing for C. belli or an empirical therapeutic trial.