The risk: Hepatitis C, which is often asymptomatic, can scar the liver and lead to cirrhosis or liver cancer, and is the leading cause of liver transplant.

What's at stake: More than 15,000 Americans die each year from hepatitis C-related illnesses, the CDC said. The CDC said testing could save 120,000 lives.

Treatment: It has been a combination of the antiviral drug ribavirin with interferon, an immune-boosting protein. A new class of drugs were introduced last year called protease inhibitors, which attacks the virus. They have been shown to cure more patients in less time with fewer side effects, but they still must be combined with interferon. Scientists are working on an experimental drug class called nucleotide polymerase inhibitors, which bind to a different part of the virus and could be used without interferon.

More: www.cdc.gov/hepatitis/C/index.htm