Abstract: Infection remains a significant complication after solid organ transplantation (SOT). The incidence of various pathogens varies widely depending on the presence of specific factors, according to which patients can be classified into different risk categories that may merit tailored prophylaxis strategies. Both the endogenous origin of microorganisms (previous colonization or latent infection) and new acquisition (primary infection from donor or environment) should be considered. Bacterial infections predominate in patients with complex hospital stays or anatomical alterations. Viral infections, caused both by opportunistic (CMV, EBV, BKV, etc.) and common viruses (influenza, respiratory virus, VVZ, etc.), are of great importance, and may contribute to chronic rejection. Fungal infections are uncommon nowadays, but cause high mortality and deserve prophylaxis for a subset of patients. Parasitic infections are a clear threat, mainly in transplanted patients or those travelling to endemic areas. Physicians attending SOT recipients should be aware of these risk factors, which include specific host characteristics, type of transplantation, microorganism and immunosuppressive policy.
