Microbial Cell-Free DNA Sequencing in the Identification of Rhizopus Arrhizus in an Adolescent With Gastrointestinal Mucormycosis

Mucormycosis is a rare and often fatal angioinvasive fungal infection, typically occurring in immunocompromised hosts. Gastrointestinal mucormycosis (GM), a rare manifestation of mucormycosis, is particularly challenging to diagnose due to its non-specific clinical presentation and overlap with other abdominal pathologies. We report the case of a previously healthy 15-year-old male with Class I obesity who presented with perforated appendicitis and developed septic shock and multi-organ failure for which he was admitted to the pediatric intensive care unit. Upon arrival, the patient was intubated and placed on mechanical ventilation. He was started on vasopressor support and intravenous antibiotics. An orogastric tube was placed for bowel decompression, but on hospital day 2, he developed profuse bloody output from the orogastric tube. Imaging revealed mixed-density debris surrounding the gastric lumen. His condition deteriorated with ongoing fevers and signs of gastrointestinal bleeding. Conventional infectious disease tests were unrevealing. Metagenomic next-generation sequencing of plasma cell-free DNA (Karius test) detected <i>Rhizopus arrhizus</i>, leading to the initiation of antifungal therapy with liposomal amphotericin B and posaconazole. Exploratory laparotomy revealed necrotic ulcers, extensive gastric and bowel necrosis and infarctions, confirming GM. Despite aggressive antifungal treatment and surgical debridement, the patient ultimately succumbed to his disease. This case underscores the importance of considering mucormycosis in critically ill patients without traditional risk factors and highlights the utility of microbial cell-free DNA sequencing as a non-invasive diagnostic adjunct in children with mucormycosis when tissue sampling is impractical.