Respiratory microsporidiosis caused by Enterocytozoon bieneusi in an HIV-negative hematopoietic stem cell transplant recipient

•Enterocytozoon bieneusi causes respiratory infections in transplant recipients.•Symptoms of respiratory E. bieneusi microsporidiosis are non-specific.•Albendazole does not eradicate E. bieneusi infection. A 23-year-old, HIV-negative woman who had undergone a hematopoietic stem cell transplantation was admitted to the hospital with respiratory failure and symptoms of bronchiolitis obliterans. A chest computed tomography scan revealed diffuse ground-glass opacification and fibrous plugs. Due to worsening respiratory failure despite treatment, ventilation was provided through a tracheostomy tube. Molecular examination of bronchoalveolar lavage and urine revealed Enterocytozoon bieneusi infection. After treatment with albendazole the patient gradually improved, but the pathogen was not eradicated and reappeared on follow-up examination. E. bieneusi belongs to the most clinically important microsporidial species infecting humans, mostly those who are immunocompromised. This fungus tends to infect enterocytes of the intestine, and there are limited studies concerning its extraintestinal location. This is the first report of a case of disseminated respiratory and urinary E. bieneusi infection in a transplant recipient.