This week, the Centers for Disease Control and Prevention (CDC) revealed a new estimate of the number of Americans living with hepatitis C. That number -- 2.4 million -- is a dramatic drop from the CDC's prior estimate of 3.5 million, which was released in 2015.
On the surface, a 1.1 million drop in the prevalence of hepatitis C in the U.S. would seem to signal a major victory for the advances made in hepatitis C treatment this decade. But in reality, 85% of people diagnosed and living with hepatitis C are not getting treated and cured with these expensive new drugs each year, according to the nonprofit Initiative for Medicines, Access and Knowledge, Inc. (I-MAK). Meanwhile, acute cases of hepatitis C tripled from 2010 to 2016, driven mostly by the opioid epidemic.
Ultimately, the CDC's new estimate "is not directly comparable" to its prior estimate, due to "methodological differences" in the way the two numbers were derived, said CDC spokesperson Paul Fulton, Jr.
Both the 2015 and 2018 estimates began with an analysis of the National Health and Nutrition Examination Survey (NHANES), a nationwide survey that uses interviews and physical examinations to create a snapshot of the nation's health.
But there are notable differences between the two estimates. They used different methods to try to account for hepatitis C infections that are not included in the NHANES data, including those in populations with high rates of hepatitis C, such as people who are incarcerated or homeless.
The first estimate was derived from NHANES data collected from 2003 to 2010, before the new generation of direct-acting antivirals was approved. That estimate also included children, adolescents, and adults, while the 2018 estimate only included those over 18 years old, meaning fewer individuals were ultimately counted.
The 2015 research was a collaborative effort by the CDC, Treatment Action Group, National Development and Research Institutes, Beth Israel Medical Center, and Weill Cornell Medical College. In addition to NHANES data, researchers estimated prevalence for groups who were not included in that dataset. Specifically, they estimated prevalence among people who were incarcerated or homeless, Native Americans living on reservations, and people in hospitals -- ultimately determining that there were about 800,000 infections in these groups.
In total, researchers concluded that the number of U.S. residents who have ever contracted hepatitis C "is probably at least 4.6 million." Of those, some spontaneously cleared their infection and some were treated successfully, meaning that "at least 3.5 million are currently infected … [though] the true prevalence could well be higher."
Three years later, CDC research sought to update this estimate, teaming up with researchers at Rensselaer, Emory University, and the Task Force for Global Health. Once again, they called on the NHANES database, but this time pulled data from 2013 to 2016, therefore potentially capturing the early wave of patients cured after U.S. Food and Drug Administration approvals of a class of hepatitis C drugs known as direct-acting antivirals began in 2011.
In addition to NHANES data, researchers estimated hepatitis C prevalence among incarcerated people, homeless people, active-duty military personnel, and nursing home residents. Ultimately, the 2018 data found that 4.1 million U.S. adults had hepatitis C antibodies in their blood, meaning they had been exposed to the virus. In total, 2.4 million had an active infection from 2013 to 2016.
While the methodological differences between the two estimates may account for some of the difference, that doesn't tell the whole story, according to Fulton.
"There has likely been a [real] decline in hepatitis C prevalence in recent years, but it is difficult to quantify precisely how much," Fulton said.
Some of this decline is likely thanks to increased availability of hepatitis C antivirals, which have dropped in price by more than 70% since they were first launched. And some of the drop may have to do with the fact that the majority of people with hepatitis C are baby boomers, many of whom have died since 2010 -- the cutoff period of the prior estimate.
Unfortunately, "because of very limited resources and systems for tracking HCV in the United States, we also can't say for sure what's driving the decline," Fulton said.