Leonard has observed one other intriguing characteristic of E. rostratum in his lab: The fungus can grow from a single spore to a lawn of freshly spore-crowned fungal filaments on a piece of dried leaf in two days flat—faster and more abundantly than any other related species he studied. "This is a fungus very well-adapted to colonizing senescent or dead leaf tissue once conditions are right," Leonard says. "So that would be another reason E. rostratum would be a likely candidate for showing up in a messy lab."
But if the fungus is primarily tropical and subtropical, what was it doing in a place like New England?
In the summer the fungus can probably find ideal growing conditions in places in the northern U.S., Leonard explains, or it may be spread northward by winds. The spores have a static electricity–based ejection system designed to launch them into the air with ease. And plentiful lawn clippings provide an ideal place for the fungus to grow.
Roberts says the group of fungi pigmented with melanin (which includes E. rostratum)—the same molecule that darkens and protects human skin—seem to be generating more human infections for reasons he does not understand. E. rostratum, in addition to causing soft-tissue infections, has also rarely provoked sinus or eye infections, primarily in immunocompromised patients.
Although the identity of the fungus surprised him, Roberts was not surprised by its ability to capitalize on its situation once inside a patient. After the fungus was injected along with the drug into the epidural space—the space between the dura mater, which encloses the spinal fluid and spinal cord, and the inside walls of the vertebrae—the fungus's filaments were able to penetrate the dura mater, enter the spinal fluid and travel straight to the brain, an environment where the immune system has a very difficult time eliminating or even just controlling infection. "Spinal fluid is a great culture medium—one of the best," he says. "The nutrients are there, and the temperature is certainly right."
Those who suffered the worst infections, he speculates, were probably those in whom the needle accidentally penetrated the dura mater, thereby shortening the fungus’s deadly path into the spinal fluid. Then, in some fatal cases, the fungal filaments began to grow in the brain, attracting platelets and white and red blood cells to aggregate around the filaments and form a mass that could block a blood vessel and initiate a stroke. Strokes were not implicated in all the fatalities, however, so the mechanism(s) in those other deaths remains unclear.
The fungus's confinement to just three lots of the drug also remains unexplained. If the facility's water or air supplies in general were contaminated, one would expect all lots to be affected. Perhaps something blew in from a nearby recycling center or some other source on one or a few days and not on others, Roberts speculated.
Another pathway could be the drug itself: Although the water used for making up the final doses was allegedly sterile, the steroid drug ingredient was not. "Using nonsterile components [for injection] in somebody's spine?" Roberts says. "My goodness, that's terrible."