A 12-month-old girl with a serious immune system disorder called HLH developed a rare and dangerous fungal infection called mucormycosis. Despite receiving the best available treatments, the fungal infection spread throughout her digestive system and caused a perforation (hole) in her intestines. The doctors found it difficult to diagnose the fungal infection early because the warning signs were subtle, and the infection progressed very rapidly. Unfortunately, the girl passed away despite emergency surgery and high-dose antifungal medications.