The number of people who die from HIV-related causes each year in the U.S. is now down to about 12,700—from a peak of more than 50,000 in the mid-1990s—thanks to condom education and distribution campaigns, increased testing and improved treatments. But now a different infectious disease is quietly killing even more people than HIV is: Hepatitis C.

The majority of the 3.2 million people who are estimated to have chronic hepatitis C virus (HCV) in the U.S. are baby boomer adults.

And most of those infected with the virus do not know that they have it, which means they could easily be spreading it to others via exposure to blood—or, occasionally, sexual contact.

Although long-term intravenous drug users are at particular risk, so are "those who experimented with [such] drugs for a limited time in their youth," Harvey Alter and T. Jake Liang, both of the National Institutes of Health, wrote in an essay published online Monday in Annals of Internal Medicine. "These bygone experiences do not often connote risk to the affected persons nor serve as a reason to seek testing," they noted, making this slow-developing disease difficult to catch before it develops into cirrhosis or liver cancer (hepatocellular carcinoma). Their essay was part of a four-paper special series on hepatitis C.

More than 15,000 people died from hepatitis C-related issues in the U.S. in 2007—about three quarters of whom were people aged 45 to 64, according to Alter and Liang. And that number is expected to double as the bulk of the population with the disease get older. The cost of treating all of these people is likely to top $6.7 billion in the decade of 2010 to 2019.

Much of that growth is anticipated because those infected with hepatitis C often don't seek treatment until the disease has caused serious damage, according to another paper published Monday in the same issue of Annals of Internal Medicine. "Hepatitis C virus infection is often asymptomatic or causes nonspecific symptoms (depression, arthralgia and fatigue) for decades," Kathleen Ly, of the U.S. Centers for Disease Control and Prevention (CDC), and her colleagues wrote in their paper.

The good news for those who do get diagnosed is that new hepatitis C drugs are coming onto the market. But they are not cheap. One new promising one, a protease inhibitor called boceprevir, runs about $1,100 per week, which when added to the double-drug cocktail of interfearon and the antiviral ribavirin, makes for especially expensive treatment. Some researchers have proposed that testing patients for a genotype that has a cure rate of less than 40 percent with previous treatment might help make treatment the more cost effective.

A new analysis in the same issue of Annals of Internal Medicine, led by Shan Liu of the Center for Health Policy at Stanford University, found that giving HCV patients of all genotypes a triple-drug cocktail is, indeed, cost-effective for allowing patients to live longer, healthier lives. And as Alter and Liang pointed out, as opposed to HIV or even hepatitis B, HCV can often be effectively cured after six months to a year of antiviral treatment. "Every effectively treated high-risk individual diminishes the infectious pool and the likelihood of secondary transmission."

With treatment options expanding, many researchers are turning their attention back to the question of locating patients. "As innovative treatments for hepatitis C follow their now-destined progression, the most burning question will not be whether to treat, but rather how to identify the many chronic HCV carriers who are unaware of their infection and are at risk for cirrhosis, end-stage liver disease, or hepatocellular carcinoma," Alter and Liang wrote.

Knowing that those born between 1945 and 1964 are at the highest risk for HCV infection could help guide screening, according to another study published in the same issue of the journal, led by David Rein, of the CDC. "Because HCV progresses slowly, the risk for serious complications is increasing among infected Americans as time passes," he and his colleagues wrote. "Without changes in current case identification and treatment, deaths from HCV are forecasted to increase to 35,000 annually by 2030."