The spread of hepatitis C virus (HCV) in North America peaked between 1940 and 1965, according to research published in the March 30 advance edition of Lancet Infectious Diseases. The investigators attribute the rapid spread of the infection to hospital transmissions and reuse of medical injection equipment rather than risky behaviors such as injection drugs, unsafe tattooing, and unprotected sex.
“Based on our results, the oldest members of the demographic cohort with the highest burden of hepatitis C virus (the baby boomers) were roughly 5 years of age around the peak of the spreads of genotype 1a in North America in 1950,” commented the authors. “Thus, it is unlikely that past sporadic risky behavior (experimentation with injecting drug use, unsafe tattooing, high risk sex, travel to endemic areas) was the dominant route of transmission in this group.”
Up to 6 million individuals in North America are infected with HCV. Approximately three-quarters of these infections involve people born between 1945 and 1965 — the Baby Boomer generation. Previous studies have identified infected blood products and experimentation with injection drug use as the main factors driving the spread of HCV in this age group. However, how and when HCV reached such high prevalence in the 1945-1965 birth cohort remains unclear.
Jeffrey Joy and colleagues from the British Columbia Centre for Excellence in HIV/AIDS and the U.S. Centers for Disease Control and Prevention (CDC) therefore analyzed 45,316 sequences of HCV genotype 1a — by far the most common HCV strain in North America. Using a technique called phylogenetic analysis they focused on 5 HCV genes to reconstruct the dynamics of the HCV epidemic in North America.
Analysis of all 5 gene regions suggested that the greatest expansion of the epidemic occurred between 1940 and 1965. The massive growth of the epidemic had subsided by 1965 and plateaued between 1965 and 1989. There was a drop in the number of new infections in the 1990s, followed by a modest increase from 2000 onward.