A viral killer more powerful than HIV could be lurking inside hundreds of thousands of American seniors. Nobody in the so-called baby boomer generation can assume they’re not infected.

That is the message acclaimed doctors Camilla Graham and Daniel Fierer want to get across on World Hepatitis Day (July 28th). Hepatitis C is a silent killer that can hide inside a person’s body for decades before causing symptoms like fatigue and yellowed skin. By then, treatment may be too late.

“We have a crisis of enormous proportions brewing," said Fierer, of Mount Sinai Hospital in New York. "There are at least a million Americans who have no idea that they have hepatitis C.”

He noted that hepatitis C, a disease of the liver, can be stealthy. Even early cirrhosis, or liver scarring, a result of advanced hepatitis C, causes no symptoms. "But once somebody has cirrhosis, he or she has an increased risk of liver cancer, and then will progress to becoming sick from the cirrhosis, at which time even with a cure, a person never will return to good health,” Fierer said.

He urges boomers to not waste one more minute before getting tested. "When I say as soon as possible, we do not have a decade to do this — we do not have the luxury to wait that long,” he said.

The  (CDC) have found that people born between 1945 and 1965 are more than five times more likely than other adults to be infected, and they represent three-quarters of all hepatitis C cases in the U.S. The CDC believes "millions" of cases remain undiagnosed.

That is why  get tested. If the infection is caught early enough, remarkable new treatments can cure the disease, once an almost certain death sentence without a liver transplant.

Ask a Specialist About New Hepatitis C Treatments »

Why Are Baby Boomers at Risk?

According to the CDC, we don't know precisely . Graham, an assistant professor at Beth Israel Deaconess Medical Center in Boston, believes that about half got it from snorting drugs such as cocaine or from injection drug use.

But these aren’t typical drug abusers. “We’re not going to find [baby boomers] with hepatitis C combing through drug rehab centers or STD clinics, places where we might currently look to find those engaged in high-risk behavior,” she told Healthline. “We’re not talking about someone under the bridge injecting heroin. These are people who maybe experimented a couple of times in college, so this is not who they are now.”

If someone asks them, “Did you inject drugs?” they likely would say they had not, Graham added. “Those people no longer identify with that youthful person, because they’re 55, and because of the stigma around these things,” she said.

Those at risk are not limited to former drug users. Others may have become infected from getting a tattoo, having a blood transfusion, or even during a hospital stay.

Before the HIV epidemic emerged in the 1980s, medical equipment wasn’t sterilized as thoroughly as it is now, Graham said. Dangerous infections can still be spread in healthcare settings, but the good news is that due to advanced testing techniques, infections are now caught earlier.

Graham said she hopes all seniors will ask for the test because doctors may not otherwise offer it. “[Doctors] that have been seeing people in their practice for 10 or 15 years, showing up and are good patients who never have been tested, but with no identifiable risk factors, it never would occur to them that they should be tested. And it could be hiding anywhere,” she said.

Read More: Am I at Risk for Hepatitis C? »

Not Me! Yes, You

Beth Israel Deaconess, Harvard University’s teaching hospital, screens all boomers for hepatitis C. In Massachusetts, electronic medical records automatically prompt doctors to test for the disease if a test has not yet been conducted. Of about 20,000 people screened at the hospital during a 10-month period ending in April, about 500 tested positive, Graham said.

Of those tested, two-thirds were boomers. The number of boomers being tested has about tripled since the CDC issued its recommendation, Graham said.

Testing is easy. A simple test for hepatitis antibodies is first administered. If that comes back positive, a follow-up test is given to measure the patient's viral load.

“We have a crisis of enormous proportions brewing. There are at least a million Americans who have no idea that they have hepatitis C.” — Dr. Daniel Fierer, Mount Sinai Hospital

Hepatitis C is more common in men than in women. Women are also more likely to spontaneously clear the virus out of their bodies, even though the antibodies linger.

“This is a men’s health problem,” Graham said, though she stressed that female boomers need to get tested, too. “Don’t try to predict by thinking ‘I was never in Vietnam, I never injected.’ Just go ahead and get tested.”

More than 2.7 million Americans are estimated to be living with hepatitis C — almost three times as many as are living with with HIV.

Besides boomers, those at increased risk include drug users, particularly those who inject, but also those who share straws when snorting. Men who have sex with men also are at high risk. Recent research has shown a significant number of HIV and hepatitis C co-infections. Fierer, the force behind that research, presented his findings this week at the 20th International AIDS Conference in Australia. 

Public health officials are battling a rise in hepatitis C infections, largely because of people injecting opiates. Even young people are doing it, Graham said. As a result, aggressive campaigns are being developed to target them as well. “These are white, suburban kids that are getting infected,” she said.

Read More: Research Shows that Hepatitis C Can Be Spread via Sex »

A Very Costly Cure

The renewed push for hepatitis testing is due in part to new treatments that can cure hepatitis C if it is caught before it presents chronic symptoms.

Although treatments vary for different genetic strains of the virus, a new drug called Sovaldi has been hailed as a breakthrough. The medication can cure the disease in about 12 weeks, but at an average cost of $84,000 for one treatment cycle, or $1,000 per pill.

“The emerging concerns, of course, worldwide, are about being able to pay for this finally effective treatment," Fierer said.

Gilead, the maker of Sovaldi, has maintained that the drug is expensive because the pharmaceutical giant pumped billions of dollars into acquiring the company that developed the drug and bringing it to market. Even at a cost of $84,000, the medication costs less than a liver transplant and can put an end to future hepatitis C complications that require hospitalization and treatment.

Previous treatments had low cure rates and severe side effects compared to Sovaldi. But the cost of the medication has alarmed insurers and governments alike, particularly given the number of people who could benefit from the drug.

Learn About Hepatitis C Medications, Costs, Side Effects, and More »

In a letter earlier this month to Gilead, U.S. Senator Chuck Grassley (R-Iowa) asked pointed questions about the price of the medication and asked for several related documents. Grassley is concerned that the government may be overpaying through Medicaid, its insurance program for the poor, and Medicare, its program for seniors.

“The large patient population combined with the high price of each individual treatment creates a question as to whether payors of healthcare, including Medicare and Medicaid, can carry such a load," the letter stated. "Healthcare experts recently estimated that Sovaldi alone could increase Medicare’s spending on prescription drugs by $2 billion between 2014 and 2015 if just 25,000 patients enrolled in the program’s prescription drug benefit, known as Part D, receive prescriptions.”

The letter goes on to note that if three times that many Medicare Part D enrollees took the drug, the cost would increase by $6.5 billion, resulting in an 8 percent premium increase for all Part D participants.

In an opinion piece published this week in the Journal of the American Medical Association, doctors Troyen Brennan and William Shrank called Sovaldi an "outlier" because of its high cost and the large population of people needing treatment. "The simple math is that treatment of patients with [hepatitis C] could add $200 to $300 per year to every insured American’s health insurance premium for each of the next five years," they wrote.

As governments debate cost-cutting measures and other pharmaceutical companies test their competing medications, the emphasis remains on testing and treatment. The World Health Organization recently launched its “Hepatitis: Think Again” campaign to educate the world about all types of hepatitis — A, B, C, D, and E. And the CDC offers a list of frequently asked questions about hepatitis C on its .