It's not known if all or just some of the vials were contaminated, or how many doses were administered for back pain or for other reasons. Those given joint injections are not believed to be at risk for fungal meningitis, which is an inflammation of the lining of the brain and spinal cord. A back injection would put any contaminant in more direct contact with that lining.
Symptoms of meningitis include severe headache, nausea, dizziness and fever. The CDC said many of the cases have been mild, and some people had strokes. Symptoms have been appearing between one and four weeks after patients got the shots, but CDC officials Thursday warned at least one illness occurred 42 days after a shot.
The fungus is difficult to grow in lab analyses, and health officials on Thursday issued an unusual piece of advice to doctors: If a patient who got the injection starts to develop meningitis symptoms, he or she should be treated, even if testing is negative for the fungus.
The fungus behind the outbreaks was initially identified as aspergillus, but as more testing of patients has been completed, it's become clear that another fungus -- a kind of black mold called exserohilum -- is the primary cause. As of Wednesday, CDC's fungal disease laboratory confirmed exserohilum in 10 people with meningitis and aspergillus in just one.
Exserohilum is common in dirt and grasses, but this is the first time it's been identified as the cause of meningitis, said Weber, who is managing the CDC's response to the outbreak.
Health officials are hurriedly trying to determine the best way to treat this kind of an illness, and have settled on two very strong anti-fungal medications. Consulting with experts, they're making a best guess as to the dosage and length of time patients will have to be treated.
"This is new territory," Weber said.
Fungal meningitis is not contagious like the more common forms.