Patients who are most vulnerable to developing PCP are severely immunocompromised following allogeneic hematopoietic stem cell transplantation or solid organ transplantation, those with hematological malignancies undergoing immunosuppressive chemotherapy, as well as patients with rheumatologic disorders and those with HIV infection (CD4 count ˂ 200 cells/μL) [2,3,4,10]. Here, CD4 is linked to pneumocystosis.