All patients received ISA as primary AFP;7.6% of patients (11/145) developed proven/probable b-IFDs, 1/11 occurred post-HSCT (probable IA);Not routinely assessed, ISA trough levels were obtained within 72 h of b-IFD in 5/11 cases (5/5 breakthrough IA) with a median of 3.7 μg/mL (range, 3.3–6.3 μg/mL);Probable b-IFDs: six probable IA, one probable mucormycosis (Syncephalastrum racemosum), one probable Fusarium dimerum infection;Proven b-IFDs: two fungemia (one C. glabrata, one Fusarium spp.), one proven mucormycosis (Rhizopus microspores). The gene discussed is AFP; the disease is infection.