A rare myeloproliferative neoplasm characterized by stem-cell derived clonal over proliferation of mature myeloid lineages, such as erythrocytes, leukocytes, and megakaryocytes, with variable degrees of megakaryocyte atypia, associated with reticulin and/or collagen bone marrow fibrosis, osteosclerosis, ineffective erythropoiesis, angiogenesis, extramedullary hematopoiesis, and abnormal cytokine expression.

A type of infection that is regarded as a sign of a pathological susceptibility to infection. There are five general subtypes. (i) Opportunistic infection, meaning infection by a pathogen that is not normally able to cause infection in a healthy host (e.g., pneumonia by Pneumocystisjirovecii or CMV); (ii) Unusual location (focus) of an infection (e.g., an aspergillus brain abscess); (iii) a protracted course or lack of adequate response to treatment (e.g., chronic rhinosinusitis); (iv) Unusual severity or intensity of an infection; and (v) unusual recurrence of infections.