Given the sky-high expense of hepatitis C virus (HCV) treatment, many insurers have restricted coverage to those with more advanced liver damage. The reason for payers’ reluctance to provide broad access to antiviral therapy is likely that a substantial number of those with hep C urgently need treatment for the virus because they have more severe liver injury. This group’s treatment costs alone pose a massive short-term financial burden.

According to a new study from the Centers for Disease Control and Prevention (CDC), about one in four of the estimated 3.5 million U.S. residents living with hep C have advanced fibrosis (scarring) or cirrhosis of the liver. This puts perhaps 800,000 people in that upper tier of people most in need of HCV-related care and treatment.

“Even though the guidelines say to treat everyone, this is a group that is most at risk of complications,” says the study’s lead author, R. Monina Klevens, DDS, MPH, director of research and evaluation in the Bureau of Infectious Disease and Laboratory Sciences at the Massachusetts Department of Public Health, who was with the CDC when the study was conducted. “It’s more urgent to address these people, to make sure they’re in medical care and to determine whether they’re eligible for treatment.”

Serious health risks associated with having hep C and advanced liver damage include liver failure, liver cancer and death. On the bright side, immediate hep C treatment can lower the risk of such outcomes, and today’s drugs have cure rates in the 95 percent–plus range.

Meanwhile, the virus recently became the No. 1 killer among all infectious diseases in the United States. People with hep C who die are on average 25 years younger than those without the virus. But a recent study found that those cured of the virus who did not drink heavily or use injection drugs had a survival rate comparable to that of the general population.

“More people die from hepatitis C than from all other infectious diseases reported to CDC combined,” says Scott Holmberg, MD, MPH, chief of the epidemiology and surveillance branch in the CDC’s Division of Viral Hepatitis and one of the coauthors of the study, which was published in Clinical Infectious Diseases. “We must take action to save lives. Testing those at risk for hepatitis C is the first step toward treating and curing those infected. It is critical that providers screen patients for risk and help those infected connect to health care.”

Klevens’s research suggests that perhaps only half of those diagnosed with chronic hep C are even in regular medical care. Furthermore, her team did not find a strong association between individuals’ severity of liver damage and the likelihood that they were in care.

Looking to determine the overall burden of advanced liver damage among the U.S. hep C population, the CDC researchers analyzed a trove of data from the laboratory testing giant Quest Diagnostics covering a four-year period between January 2010 and December 2013.

To estimate the severity of individuals’ liver damage, investigators calculated the aspartate aminotransferase (AST, a liver enzyme)-to-platelet ratio (APRI) as well as the fibrosis-4 (FIB-4) scale, which factors in age, AST, platelets and alanine aminotransferase (ALT, another liver enzyme). About half of those with current hep C infection had the necessary lab tests conducted within 90 days of their first HCV test.

Relying on APRI and FIB-4 gave the researchers access to a much larger data set than if they had based their analysis on liver biopsy results.

The study authors found their results were consistent regardless of whether they based them on APRI or FIB-4. So ultimately they just relied on the latter scale. Research into FIB-4’s accuracy has found that its results are particularly good at determining whether someone has advanced fibrosis or cirrhosis.

The CDC team analyzed the results of about 10 million hep C tests, which covered 5.6 million individual people. Of the 2.6 million people for whom there was data to estimate their level of liver disease, 5 percent (293,000 people) were currently infected with HCV. An additional 60,000 were either cured of or had spontaneously cleared the virus (some people clear hep C on their own during the first few months after infection).

The study’s overall data sample was quite massive but didn’t necessarily yield a representative sample of the hep C population as a whole. Quest provides lab testing to about half of U.S. physicians and hospitals. Between 2012 and 2014, the CDC asked six health departments across the country to determine which lab had conducted new hep C diagnoses. The proportion of those test results coming from Quest ranged between 11 and 73 percent. So according to Klevens, the representativeness of the data in this new study varied from state to state.

An additional limitation of the study is that no testing source can provide data on the sizable population never tested for hep C.

Overall, 22 percent of those with current HCV infection had an FIB-4 score of greater than 3.25, indicating advanced fibrosis or cirrhosis (including 27 percent of baby boomers, those born between 1945 and 1965). This statistic was within the ballpark of the findings from previous studies. By comparison, the CDC paper found that 11 percent of those with resolved or cured infection and 3 percent of those who were never infected had such advanced liver damage.

Just 54 percent of those currently infected with hep C were in care for the virus. The study authors defined people as in care if within six months of an RNA test confirming chronic HCV infection, they had certain lab tests conducted or an infectious diseases or gastroenterology specialist ordered any test on their behalf. Moreover, half of those with current hep C had genotype testing conducted during the four-year study period, indicating they were evaluated for antiviral treatment.

After adjusting their data for various factors, the researchers could not find any variables strongly associated with being in hep C care or with being evaluated for treatment of the virus.

Given that many of those with current hep C who were not in care were tested by primary care physicians, the study authors echoed a common call that such clinicians be trained in HCV treatment, management and hep C-related referrals to specialists.

The fact of the matter is, because the hep C population is so immense, there are simply not enough medical specialists to handle the caseload. Consequently, much of the burden of care and treatment for those living with the virus will likely fall to primary care physicians.

Klevens stresses the importance of ongoing medical care for those with hep C not just to monitor the liver and consider treatment for the virus but also to promote overall health and well-being.

“Even in areas where treatment with antivirals is not feasible,” she says, “still there are people who need to be in care because of the opportunity for counseling for alcohol use, for example, and other aspects of care.”

Most clinicians discourage drinking of any kind among those with hep C, due to alcohol’s potential for speeding up liver damage. They advise that, at the very least, people cut back as much as possible.