Environmental phase morphology of Coccidioides in blood culture: a case report

ABSTRACT Background Coccidioides species are dimorphic fungi that exist in distinct morphological forms depending on environmental conditions, such as temperature. The parasitic phase, consisting of endosporulating spherules, is expected in vivo , while mycelial forms with arthroconidia seen in the environmental phase are expected at comparatively lower temperatures than mammalian body temperature. The incidence of Coccidioides fungemia is low but well documented in adults in cases of severe disseminated disease. The morphological description of Coccidioides spp. isolated from blood culture is limited in the published literature. Case Summary We present the case of a 59-year-old man with a history of allogeneic hematopoietic stem cell transplantation who developed disseminated coccidioidomycosis with positive cultures from blood and bronchoalveolar lavage specimens. During laboratory work-up, blood cultures initially demonstrated septate hyphae on Gram stain of the broth isolate, which was subsequently identified as Coccidioides immitis/posadasii . The initial Gram stain result raised concerns of other mold infections, given the assumption that Coccidioides appears as the spherular rather than environmental mold form at body temperature. Conclusion This case highlights the unexpected persistence of environmental phase morphology of Coccidioides spp. in blood culture despite incubation at 35°C, demonstrating that temperature alone is insufficient to trigger the parasitic phase transition and that additional host-specific factors are required for spherule formation.