Cluster of Herbaspirillum spp. bacteremia among patients with solid tumors in a tertiary cancer center: clinical characteristics and infection control implications.

OBJECTIVES: Herbaspirillum species are environmental, nonfermenting Gram-negative bacilli that are increasingly recognized as opportunistic pathogens in immunocompromised hosts. We describe a cluster of Herbaspirillum spp. bloodstream infections at a tertiary cancer center in Muscat, Oman. METHODS: We investigated a cluster of Herbaspirillum aquaticum bloodstream infections identified among hospitalized patients at a tertiary cancer center between May and August 2025. Clinical and epidemiological data were reviewed retrospectively. Bloodstream infections were classified according to Infectious Diseases Society of America criteria for central line-related bloodstream infection. Isolates were identified using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Environmental sampling was conducted in patient-care areas, water systems, and commonly used medications. Molecular relatedness among isolates was assessed using pulsed-field gel electrophoresis. RESULTS: Five cases of H. aquaticum bloodstream infection were identified over a 4-month period. The median age was 53 years (range, 40-62), and 3 patients (60%) were male. All five patients (100%) had underlying malignancies and had undergone recent surgical or invasive procedures. Four of the five cases (80%) met Infectious Diseases Society of America criteria for central line-related bloodstream infection. Pulsed-field gel electrophoresis was performed on four of the five available isolates (80%) and demonstrated indistinguishable banding patterns, supporting clonal relatedness and suggesting a common source. Extensive environmental sampling did not identify a definitive reservoir. A shared normal saline solution used during medication preparation was considered a possible source; however, culture was negative. After the practice of using shared saline was discontinued, no additional cases were identified. Clinical recovery occurred in four patients (80%). One patient experienced recurrent bacteremia, and one patient died in the setting of polymicrobial septic shock. CONCLUSION: H. aquaticum is an uncommon but important cause of health care-associated bloodstream infection in patients with cancer. Its recognition should prompt timely microbiological confirmation and careful evaluation of potential health care-associated sources, particularly when clustered cases occur in high-risk units.