"I am weaker than I ever have been," Johnson, 55, said in his Capitol Hill office.
According to the Centers for Disease Control and Prevention, hepatitis C is transmitted when clean blood comes in contact with blood infected by the disease. Between 3 million and 4 million people in the United States have the disease today, and many more may not even know they have it because it can lie dormant for decades.
Before 1992, hepatitis C was commonly transmitted through blood transfusions. Today, with improved blood screening, the most common mode of transmission is through injection drug use, but it also can be spread by other means, such as through contaminated razor blades or dirty tattoo needles or by coming into contact with infected blood in other ways. It also is occasionally transmitted through sex, or from a mother to a child, said Dr. John Ward, director of the CDC's division of viral hepatitis in Atlanta.
Johnson said he first learned he had the disease in 1998. He said he does not know how he contracted it.
With Mereda Davis Johnson, his wife of more than 20 years, seated beside him in his Capitol Hill office, Johnson said he has never used intravenous drugs or engaged in any other sort of risks that could have caused him to get the disease. He also said he has never had a blood transfusion.
"I have no idea," he said when asked how he contracted the disease.
Mereda Davis Johnson said the disease has been the most difficult challenge she and her husband have ever faced. She said she gets checked regularly for the disease, and that it has not spread to her or either of the couple's two children.
"This has been the most difficult challege for him ever," said Mereda Davis Johnson, an Atlanta area attorney. "I know I could not do it. But Hank is tough."
Rep. Johnson decided to disclose he had the disease after the AJC asked him about it amid rising questions about his health both in Washington and in the 4th Congressional District, east of Atlanta, which he has represented since 2006.
The disease, he said, was one of the reasons he decided to run for office in the first place.
When he was first diagnosed 11 years ago, Johnson said, his doctor gave him 20 years to live.
"I determined that if I only had 20 years to live, I am going to do everything I wanted to do in life," he said.
Johnson said he got his financial affairs in order, saved some money for his family and then ran for DeKalb County Commission, serving two terms beginning in 2000. When he had the opportunity to run against former congresswoman Cynthia McKinney for the 4th Congressional District seat, he decided to do so. He beat her in a runoff election in August 2006. He was unopposed for re-election in 2008.
"The final goal I had was to be a congressman," he said.
Johnson said he doesn't worry anymore about dying. While his liver has degraded and other health problems have resulted from his treatment, he said doctors have given him no limitations on how much longer he'll live.
He is being treated at Walter Reed Army Medical Center with a combination of interferon and ribavirin, which, like cancer chemotherapy, comes with many side-effects.
"He has been a model patient, sticking with his course of treatment even when it was most difficult," his physician, Dr. Maria Sjogren, said in a statement.
Up for re-election in November 2010, Johnson said he is planning to begin campaigning for office again, in earnest, when he's done with his latest round of treatment in February. At least two Republican challengers have said they'll run for his seat.
Alan Abramowitz, a political science professor at Emory University in Atlanta, said he doesn't think that an illness such as Johnson's is necessarily damaging to a politician's career. That's especially the case in a district where they have a strong base, he added -- as Johnson has with Democrats in the 4th Congressional District.
"Certainly it's something they're going to have to deal with," Abramowitz said. "But it's my guess that if someone has a solid base in their constituency, they could survive it."
Along with seeking re-election, Johnson said he wants to become an advocate for hepatitis C victims. He said Monday he has signed on as a co-sponsor of a House bill that would establish and promote a comprehensive prevention, education and research program for viral hepatitis infections.
He also said he plans to begin working with the National Viral Hepatitis Roundtable, a coalition of more than 100 organizations that works to prevent viral hepatitis.
"On behalf of the entire chronic viral hepatitis community, we offer Congressman Johnson our support, prayers and encouragement," Martha Saly, director of the group, said in a statement. "Congressman Johnson's announcement shines a much-needed spotlight on a public-health issue that has historically resided in the shadows."
Sometimes called the "silent epidemic" because it can manifest itself in a victim for decades without showing any symptoms, hepatitis C has become better known publicly in recent years.
Numerous celebrities, including singers Naomi Judd and Natalie Cole and actors such as Pamela Anderson and Christopher Kennedy Lawford, who have been stricken with the disease, have become outspoken advocates. They encourage people to get tested regularly and they are pushing to find a cure.
Johnson said he hopes to do the same.
"There are literally millions of people walking around with this virus who do not even know they have it," Johnson said. "And once they do know they have it, the stigma of getting treated is there.
"I'm going to be a public figure who takes the stigma away from having the virus," he said.