Immunocompromised host pneumonia: a shifting landscape of risk.

Immunocompromised host pneumonia (ICHP) is an infectious pneumonia that occurs in individuals with quantitative or functional impairment of host immune defenses. The heterogeneity of immune deficiencies has further diversified the immune landscape, leading to novel patterns of infection and diagnostic dilemmas, harboring a broader, more opportunistic spectrum of pathogens, and increasing the risk of treatment failure and adverse outcomes, profoundly influencing susceptibility to pathogens, clinical presentation, and response to treatment. This review focuses on ICHP, including solid organ transplants and hematopoietic stem cell transplant recipients, patients undergoing cancer therapy, and individuals receiving immunomodulatory treatments for autoimmune diseases. These groups represent a growing segment of the population, driven by advances in transplantation, oncology, and rheumatology, but they also carry a disproportionately high burden of severe infections.