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Charlie Sheen announced this week he has the virus that causes AIDS.

More than a million people in the U.S. are infected with HIV, but according to the CDC, close to 1 in 8 don’t even know it.

Sheen’s high profile case has raised some questions.

Dr. Stephen Threlkeld is an Infectious Disease Expert and he stopped by to talk about how it’s transmitted and how to protect against it.