Biopsy tissue proved that the organism was of the fungal species Aspergillus, a rather unusual source of vertebral osteomyelitis. The Aspergillus species are ubiquitous fungi and infrequently cause infections in healthy and immunocompromised humans. Invasive aspergillosis is primarily seen in patients with immune dysfunction. The organism can infect the lungs, sinuses, airways, eyes, nail beds, foreign bodies (including catheters), operative sites, bone, kidneys, and finally the brain, when the infection is disseminated. Aspergillus is probably best known for the fungal balls or aspergillomas that can develop in the lungs, sinuses and respiratory tree. It can virtually invade any tissue in the body but only a few cases of vertebral infections have been reported.

A patient with aplastic anemia becomes susceptible to opportunistic infections while in a state of neutropenia and monocytopenia. The literature on this topic is scarce, but one NIH retrospective study of 150 patients with aplastic anemia found that invasive fungal infections were the major cause of mortality. The fungal infections were more commonly due to aspergillus than candida and typically disseminated from the lungs.