Health officials are still learning from the fungal outbreak tied to tainted steroid pain injections made at the now-shuttered New England Compounding Company.
Researchers now know that most patients' immune systems didn't try to fight off the deadly fungi as it burrowed into their spinal columns – called duras -- and wreaked havoc, according to one of two scientific journal articles published in the New England Journal of Medicine to review the outbreak.
The outbreak that sickened 750 people since last fall was unprecedented -- first, because only people who received a tainted steroid injection were at risk; and, second, because the fungus wasn't known for making people sick, let alone causing a deadly inflammatory disease and other infections that killed 64 people so far.
Dr. John Jernigan, who works at the Centers for Disease Control and co-authored one of the studies, said there are several theories about why this happened, one being that the steroids' anti-inflammatory properties staved off patients' immune systems.
"This organism was thoroughly bathed in a medication that made it more difficult for the body to fight it," Jernigan, who headed the CDC's clinical team during the outbreak. "It might have been sort of the perfect storm, if you will."
By definition, an epidural is meant to be injected into an area outside the dura – not inside it – but the fungus found a way into patients' duras, where it caused sometimes fatal infections or inflammatory disease. Jernigan said it's not likely several hundred doctors made their injections too deep.
"We're seeing the organism itself burrowing through dense collagenous barriers," he said. "There's no evidence that the body host was fighting this."
Although there have been no new infections since July, the outbreak sickened 750 patients, killing 64 of them, according to the CDC.
Click through to learn more about what officials thought they knew about the outbreak last year compared to what we know now about the "largest documented healthcare-related outbreak in the United States."
It was more than meningitis.
The investigation began in late September 2012 as a fungal meningitis outbreak, but researchers would later learn that there was more to the outbreak than meningitis.
A few months later, researchers would start to see other infections of the bone and soft tissue around the spine, said Dr. Rachel Smith, the CDC epidemiologist who authored the look-back study of how investigators handled the outbreak.
Of the 750 outbreak patients, 324 had spinal infections instead of meningitis and another 151 got spinal infections along with their meningitis, according to CDC records. Another few dozen had either a joint infection or a stroke.
Investigators eventually learned that the first case in the outbreak occurred in July and wasn't meningitis at all, according to Smith's study.
The "risk period" was not 42 days.
Although officials initially told the public that there was a 42-day "risk period" for contracting fungal meningitis, the incubation period varied much more than that, according to Smith's study.
Spanning all fungal-related illnesses, people got sick anywhere from 0 days to 249 days after receiving the tainted injections, according to the study.
It was more than one type of fungus.
Investigators initially thought people were infected with a fungus called Aspergillus, but a fungus called Exserohilum rostratum was identified in most patients, Jernigan said.
The investigation of these different fungi was hindered by the fact that medical professionals who performed the initial injections didn't write down the lot number of the compounded steroid for their records.