A Case of Severe Neonatal Neutropenia Secondary to Late-Onset Sepsis From E. coli Omphalitis.

Severe neonatal neutropenia, defined as an absolute neutrophil count (ANC) of <500/µL, is a critical hematologic finding that signals either a severe consumptive process or a primary bone marrow disorder. We present the case of an eight-day-old, full-term female infant who presented with fever and irritability, later diagnosed with severe neutropenia (ANC: 400/µL) and elevated C-reactive protein (CRP) (150 mg/L). Omphalitis was identified as the source, with pus culture growing pan-sensitive Escherichia coli, confirming late-onset neonatal sepsis (LONS). The patient was managed with targeted intravenous ceftazidime and a short course of granulocyte colony-stimulating factor (G-CSF). A comprehensive workup, including a bone marrow aspirate and whole exome sequencing (WES), was performed to rule out congenital etiologies; WES returned negative, supporting the diagnosis of acquired, sepsis-induced neutropenia. On follow-up at two months of age, the infant was asymptomatic and thriving well and had a normal complete blood count with differential (CBCD). This case underscores the importance of a systematic diagnostic approach to neonatal neutropenia, highlighting the differential diagnosis and the evolving role of advanced genetic testing such as WES in providing definitive diagnostic and prognostic clarity, thereby guiding appropriate management.