Delayed opportunistic infections in hematopoietic stem cell transplantation patients: a surmountable challenge

Changes in the transplantation procedure and the implementation of effective supportive care strategies have decreased the incidence of infectious complications early after conditioning therapy for allogeneic hematopoietic stem cell transplantation (HCT) and have extended the duration of risks later. Therefore, the types of infections that cause significant morbidity and the timing of risks have changed. These late infections are caused by all types of organisms, bacterial, viral, and fungal, but risks are predictable and surmountable with the use of tailored prevention strategies. Specifically, recent studies document prolonged risks for bacterial infections in the setting of GVHD, especially those caused by encapsulated organisms and those secondary to impaired Ab responses. Both prophylaxis and vaccination strategies can be used as a means to prevent infections, which typically manifest in the respiratory tract. Multiple viruses cause infection later after HCT, including several herpesviruses (eg, CMV and varicella zoster virus) and other respiratory viruses such as influenza and adenovirus. These infections can cause severe disease with diagnostic challenges, but prevention strategies using enhanced monitoring and/or prophylaxis may be effective. Finally, fungi also cause disease late after HCT, especially filamentous fungi (eg, Aspergillus species and Mucormycoses) and Pneumocystis jiroveci; prophylactic strategies may be used successfully to prevent invasive infection. Late infections and methods to prevent them are reviewed herein.