(CNN) -- Investigators said Thursday they found the fungus Exserohilum in one medicine lot from the compounding pharmacy at the center of a meningitis outbreak that has killed 21 people, the U.S. Food and Drug Administration announced.
The presence of Exserohilum was found in "unopened medication vials," which were tested at the Centers for Disease Control and Prevention, according to the FDA.
The discovery links the fungus to the Massachusetts-based New England Compounding Center, the FDA said.
The CDC said Exserohilum had been found in 45 patients. The fungus can be difficult to find, meaning a patient with a negative test is still not in the clear. Symptoms from Exserohilum also can take a long time to develop.
The CDC updated Friday the number of people known to have contracted noncontagious fungal meningitis from steroid injections. The number of cases has grown to 271.
Three of the cases are a "peripheral joint infection" that specifically affects a joint such as a knee, hip, shoulder or elbow, officials said.
Sixteen states have been affected, including New York, which was added to the CDC's list Thursday.
Meningitis is an inflammation of the protective membranes covering the brain and spinal cord. It is usually caused by an infection, frequently with bacteria or a virus, but it can also be caused by less common pathogens, such as fungi in this case, according to the CDC.
Fungal meningitis is very rare and, unlike viral and bacterial meningitis, is not contagious.