In the United States, the number of people who have been infected with hepatitis C virus (HCV) may have been undercounted by a whopping 1.1 million, according to a paper published in the September 2011 edition of Liver International. Epidemiologists believe that at least 5.2 million people in the United States are HCV antibody positive—meaning that they were infected at one time, although they may not have developed chronic hepatitis C—an increase of 1.1 million over The National Health and Nutrition Examination Survey (NHANES) estimate of 4.1 million cases.

NHANES samples American households. Because high-risk groups such as homeless people, prisoners and immigrants were not included, Eric Chak, MD, of the University of California at Los Angeles and his colleagues suggest in their paper that NHANES may have underestimated the number of HCV-positive people in the United States.

Chak’s team reviewed research on HCV rates among prisoners, homeless people, active military personnel and nursing home residents to determine a more accurate prevalence rate. They also cross-checked HCV rates among health care workers and people on long-term dialysis, because both groups are thought to have higher HCV rates than the general public, and both were underrepresented in NHANES.

NHANES reported an HCV prevalence rate of 1.6 percent among the U.S. general population. HCV rates in studies of high-risk populations varied, but they were always much higher than that of the general population. Among jailed and incarcerated individuals, HCV rates ranged from 23 percent to 41 percent, and HCV rates among homeless people ranged from 22 percent to 52 percent. Residents of nursing homes had an HCV rate of 4.5 percent.

Chak’s team found the highest HCV rates among HIV-positive veterans and homeless people, probably because of overlapping risk factors for each virus. People on active military duty were the only group with an HCV rate lower than that of the general population (0.48 percent) among those excluded from NHANES.
HCV was also more common among groups that were underrepresented in NHANES than the general population. The HCV rate among people on dialysis was 7.8 percent, and it ranged from 0.9 percent to 3.6 percent among health care workers.

When Chak and his colleagues compared the NHANES estimate of HCV among veterans and people who use injection and non-injection drugs to rates from other studies, they found that NHANES accurately reflected HCV rates among people who use drugs. However, NHANES underestimated the rate of HCV among veterans—whereas NHANES suggested a rate of 2.8 percent, Chak’s group’s review found the rate to be 5.4 percent to more than 10 percent.

Researchers arrived at their estimate by looking at the number of people in each high-risk group—which was derived from U.S. statistics—and the HCV rate in each high-risk group. Then, they added these figures to the NHANES estimate.

The authors noted that the new estimate underscores the importance of HCV prevention among high-risk groups.