Reuters Health Information (2010-07-22): Hepatitis C rate may be down in the U.S.: study
Hepatitis C rate may be down in the U.S.: study
Last Updated: 2010-07-22 14:05:10 -0400 (Reuters Health)
NEW YORK (Reuters Health) - A new study finds that the percentage of U.S. blood donors with hepatitis C virus (HCV) infection is substantially lower now than in the early 1990s -- in what researchers say probably reflects an overall decline in the infection rate among Americans.
The findings also hint at a link between multiple pregnancies and the virus, and of a protective effect of obesity, although it's too soon to tell whether these associations will hold up.
Since 1992, the U.S. donor-blood supply has been screened for HCV, and the risk of receiving HCV-contaminated blood is now estimated at one in 2 million, according to the National Heart, Lung, and Blood Institute.
Studies from the mid-1990s suggested that 0.5% of U.S. blood donors between 1992 and 1993 harbored antibodies to hepatitis C. The prevalence of antibody to HCV and the prevalence of HCV RNA in more recent years had been unclear, however.
In the new study, published online July 9th in the Journal of Infectious Diseases, researchers analyzed samples from nearly 960,000 blood donors at six U.S. blood banks between 2006 and 2007.
They found that 0.07% of donors tested positive for antibodies to hepatitis C, including 74% with positive HCV RNA tests.
"It's a strikingly lower prevalence" compared with 1992-1993, said lead researcher Dr. Edward L. Murphy, of the University of California, San Francisco.
The decrease, Dr. Murphy told Reuters Health, likely reflects, in part, an overall decline of hepatitis C infection among relatively younger Americans. The "Baby Boomers" born between the late 1940s and early 1960s had higher rates of injection-drug use than subsequent generations, and therefore a higher risk of HCV.
In support of such a "birth cohort effect," Murphy's team found that in 2006-2007, donors in their 40s and 50s had the highest rate of hepatitis C compared with other age groups. In the early 1990s, the highest rates had been seen among donors in their 30s and 40s.
The findings, according to Dr. Murphy, suggest that the Baby Boomer generation is likely to have the highest rate of hepatitis-C- related liver disease, and that the rate will decline among younger Americans.
"I think the message here is a positive one," he said.
Of course, Dr. Murphy added, the rate of hepatitis C among blood donors would not be reflective of that among injection-drug users, who continue to have the highest risk of hepatitis C infection among Americans.
The study also found two "novel" factors associated with a higher risk of hepatitis C infection among blood donors.
Among women, the odds of having antibodies to the virus climbed along with the number of children they had, from about one in 3,300 for nulliparous women to about one in 1,000 for women with five or more children.
Dr. Murphy cautioned that "you don't want to put too much into one finding." But it raises the possibility that some women acquire the infection during childbirth -- via contaminated instruments or during C-section, for example, he said.
The other new finding was that obese adults were less likely to have hepatitis C antibodies, and when they did, they were less likely to have viremia. The implication is that obese people may be more likely than thinner ones to clear the infection.
Dr. Murphy called that finding "surprising," and said that, as with the findings on pregnancy, more research is needed to confirm the association.
As for why obesity would potentially protect against hepatitis C, he noted that obesity is believed to involve a chronic state of low-level inflammation in the body. While that's usually a negative thing, it's possible that when it comes to hepatitis C infection, inflammation is protective, Dr. Murphy said.
Blacks were also less likely to be HCV RNA positive.
"Our intriguing results regarding an inverse association of obesity with both HCV infection and viremia may influence the direction of future research on the genetics and metabolic effects of chronic HCV infection, particularly among healthier HCV carriers, as opposed to those with preexisting liver disease," the research team concludes.
J Infect Dis 2010;202:576-584.