U.S. federal health officials say 13,000 people in 23 states may have been injected with a contaminated steroid suspected of causing the deadly fungal meningitis outbreak.

This is the first time the Centers for Disease Control have put out an actual number of patients who got the medicine. But officials say they do not know how many people are at risk for meningitis.

Some of the patients were injected with the steroid for back pain and are at the greatest risk, while others were treated for achy knee and shoulder joints and are at a lower risk.

The CDC is working with local authorities to try to identify everyone who may have gotten the infected steroid.

The number of confirmed fungal meningitis cases was up to 105 Monday with eight deaths. It can take as long as one month for symptoms to appear.

The company that made the contaminated steroid, the New England Compounding Center in Massachusetts, has recalled the steroid and was shut down.

Meningitis is a disease infecting membranes protecting the brain and spinal cord. There are five different types. Fungal meningitis is the rarest form. Other types are caused by bacteria, a virus or a parasite.