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Hepatitis C Epidemic in North America Peaked Between 1940 and 1965

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.

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"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.

Analysis of separate genes revealed a variation in the period of greatest growth, ranging from circa 1940 for NS2 to 1965 for NS4B. Overall, phylogenetic analysis most strongly suggested that the period 1948 to 1963 saw the biggest expansion of the HCV epidemic.

"In sum, our phylogenetic analyses strongly suggest that the hepatitis C genotype 1a epidemic in North America had already attained the height of its distribution by 1960," wrote the authors. "These analyses suggest the period of greatest increase in North America was substantially earlier than previously suggested."

The early expansion of the epidemic coincided with the increase in the number of medical procedures conducted during World War II and its immediate aftermath, a period when injection and blood transfusion technologies were still in their infancy.

Before 1950, injecting technology was characterized by the use of glass and metal syringes, which were sterilized manually and reused. These were phased out and replaced by disposable syringes between 1950 and 1960, and after 1960 the reuse of syringes was greatly reduced in North America. The period 1920 to 1960 also saw the expansion of recreational injection drug use and needle sharing, which peaked in the late 1960s.

The spread of HCV during the plateau period -- 1965 to 1989 -- was likely due to transfusion with contaminated blood products. Rigorous screening was only introduced in 1992, and consistent with this innovation, the investigators found a reduction in the rate of new infections after 1990.

The slight up-turn in infections after 2000 is consistent with epidemiological evidence of increases in HCV infections among young injection drug users and also HIV-positive men who have sex with men. 

"Our data indicate that the rapid and large-scale expansion of hepatitis C virus transmission in North America was coincident with increases in medical procedures that began after World War II…and not only the rise in injecting drug use, which peaked much later in North America in the late 1960s," concluded the authors. "The prevailing view that the North American epidemic is predominately attributable to past sporadic risky behaviors is not supported by our data."

The investigators hope their findings will help reduce the stigma associated with HCV infection in the Baby Boomer generation and encourage more people to access HCV screening, potentially increasing the number of patients presenting for care and effective treatment.

"Reduced stigma will facilitate widespread testing and timely access to life-saving HCV treatment," coauthor Julio Montaner said in a BC Centre for Excellence in HIV/AIDS press release. "Any baby boomer could be living with HCV even in the absence of symptoms or any history of high risk behaviors, and as such they should be encouraged to proactively seek HCV testing."

"This study demonstrates the importance of offering a [HCV] test to all Baby Boomers rather than relying on risk based testing alone," added John Ward, director of the CDC's Division of Viral Hepatitis.

4/6/16

Reference

JB Joy, RM McCloskey, T Nguyen, et al. The spread of hepatitis C virus genotype 1a in North America: a retrospective phylogenetic study. Lancet Infectious Diseases S1473-3099(16)00124-9. March 30, 2016 (online ahead of print).

Other Source

BC Centre for Excellence in HIV/AIDS. North American Hepatitis C Epidemic Peaked around 1950, 15 Years Earlier than Previous Estimates. Press release. March 31, 2016.