Cluster and sporadic cases of herbaspirillum species infections in patients with cancer

Background. Herbaspirillum species are gram-negative Betaproteobacteria that inhabit the rhizosphere. We investigated a potential cluster of hospital-based Herbaspirillum species infections. Methods. Cases were defined as Herbaspirillum species isolated from a patient in our comprehensive cancer center between 1 January 2006 and 15 October 2013. Case finding was performed by reviewing isolates initially identified as Burkholderia cepacia susceptible to all antibiotics tested, and 16S ribosomal DNA sequencing of available isolates to confirm their identity. Pulsed-field gel electrophoresis (PFGE) was performed to test genetic relatedness. Facility observations, infection prevention assessments, and environmental sampling were performed to investigate potential sources of Herbaspirillum species. Results. Eight cases of Herbaspirillum species were identified. Isolates from the first 5 clustered cases were initially misidentified as B. cepacia, and available isolates from 4 of these cases were indistinguishable. The 3 subsequent cases were identified by prospective surveillance and had different PFGE patterns. All but 1 case-patient had bloodstream infections, and 6 presented with sepsis. Underlying diagnoses included solid tumors (3), leukemia (3), lymphoma (1), and aplastic anemia (1). Herbaspirillum species infections were hospital-onset in 5 patients and community-onset in 3. All symptomatic patients were treated with intravenous antibiotics, and their infections resolved. No environmental source or common mechanism of acquisition was identified. Conclusions. This is the first report of a hospital-based cluster of Herbaspirillum species infections. Herbaspirillum species are capable of causing bacteremia and sepsis in immunocompromised patients. Herbaspirillum species can be misidentified as Burkholderia cepacia by commercially available microbial identification systems.