Iatrogenic factors, not high-risk behaviors, were the main cause of the exponential spread of hepatitis C virus infections in North America, according to a phylogenetic study published online in the Lancet Infectious Diseases.

The study shifted the epicenter of spread back by more than 15 years, to about 1950, when medical procedures were expanding after World War II at the same time that clinicians continued to reuse metal and glass syringes, said Dr. Jeffrey Joy of the British Columbia Centre for Excellence in HIV/AIDS, Vancouver, and his associates.

Exponential HCV transmission had mostly ended by 1965, negating “the idea that the epidemic among baby boomers and other demographic groups in North America is primarily due to injection drug use, unsafe tattooing, high-risk sex, and travel to high endemic areas during youth,” the researchers added.

The hepatitis C virus evolves rapidly, enabling researchers to characterize its spread based on the genetic divergence of infections. Dr. Joy and his associates studied 45,316 HCV genotype 1a sequences from the National Center for Biotechnology Information GenBank nucleotide database to carry out phylogenetic analyses of five HCV genes – E1, E2, NS2, NS4B, and NS5B ( Lancet Infect Dis. 2016 Mar 30. doi: 10.1016/S1473-3099[16]00124-9 ).

The combined results for all gene regions suggested that the North American HCV epidemic expanded the most between 1940 and 1965, and that transmission rates peaked in 1950, when the oldest baby boomers were only 5 years old. Thus, nosocomial transmission rather than risky behaviors was the likely driver behind most infections, the researchers said.

“Our results could help to reduce stigma related to screening and diagnosis of hepatitis C virus, potentially increasing the numbers of providers offering screening, patients accepting testing, and if positive, presenting for care and treatment,” the authors noted.

The researchers also found that HCV transmission rates plateaued between 1965 and 1989, and dropped in the early 1990s, coinciding with increases in blood product testing and needle exchange programs aimed at preventing HIV infections. Furthermore, HCV infections rose slightly after 2000, mirroring epidemiologic reports of outbreaks among young injection drug users in nonurban areas and among men who have sex with men, the researchers said.

The Canadian Institutes of Health Research, Michael Smith Foundation for Health Research, and BC Centre for Excellence in HIV/AIDS funded the study. The investigators disclosed no competing interests.


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