Hepatitis C attacks the liver silently, and most people don’t even know they have it until liver damage shows up decades later.

Worldwide, it’s estimated that 180 million people have chronic hepatitis C, with more than 4 million of these cases in the United States, according to the National Institutes of Health.

Among those cases is Grammy-winning singer Natalie Cole, her publicist confirmed in a statement released Wednesday.

The statement said the disease was revealed during a routine examination and was likely caused by her drug use years ago.

“Hepatitis C is a chronic disease,” Dr. Joseph Rahimian, an infectious disease specialist at St. Vincent’s Hospital in New York City, told FOXNews.com. “It can lead to liver failure or liver cancer and it takes years to happen. The sooner you know you have it, the better off you are”

In general, hepatitis C is spread through contact with infected blood. But the most common way to get it in the U.S. is by sharing needles and other paraphernalia used to inject illegal drugs, Rahimian said.

“You can also get it through sexual contact, though it appears to be an infrequent mode of transmission,” he added.

For some people, hepatitis C can go away on its own, but for the majority of people who acquire the disease, it leads to chronic liver disease.

“It’s a very difficult disease to treat, and treatment requires strong anti-viral medications for many months. And it’s not always successful,” Rahimian said.

Dr. Graham Woolf, associate clinical professor of medicine at UCLA/Cedars Sinai Medical Center, said Cole has had a "terrific response to her medication and is now virus negative."

"This gives her an increased chance of cure," he said. "But, she has also suffered significant side effects from the anti-viral medicine, which is the only FDA authorized treatment for hepatitis C. Her side effects include fatigue, muscle aches and dehydration, but she is recovering from these."

The standard treatment for hepatitis C is weekly injections of a drug called pegylated interferon alpha, combined with twice-daily oral doses of ribavirin, according to the Mayo Clinic.

“It is curable, but not everyone can be cured,” Rahimian said. You treat it for almost a year and in some people it works, but it doesn’t cure everyone. She’s lucky because treatment worked for her.”

People at risk for hepatitis C include:

— Anyone who has had a history of intravenous (IV) drug use

— Those who have had sexual contact with someone known to have hepatitis C

— Those who have received an organ transplant or drug transfusion before 1992, when improved blood-screening tests became available

— Health care workers who have been exposed to infected blood

“It’s a simple blood test that can show the presence of the virus,” Rahimian said. “While treatment is difficult, if you do manage to get through it, you will decrease your risk of liver failure and liver cancer.”

Cole, 58, the daughter of jazz legend Nat King Cole, has sold millions of records over her long career. She is due to release "Still Unforgettable," the follow-up to 1991's Grammy-winning, multiplatinum CD "Unforgettable ... With Love," on which she remade some of her father's classics, in September.

The Associated Press contributed to this report.