The spread of
hepatitis C virus (HCV) in North America peaked between 1940 and 1965,
according to research published in Lancet
Infectious Diseases. The investigators attribute the rapid spread of the
infection to hospital transmissions and reuse of medical injecting equipment rather
than risky behaviours such as injecting 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 five years of age around
the peak of the spreads of genotype 1a in North America in 1950,” comment the
authors. “Thus, it is unlikely that past sporadic risky behaviour (experimentation
with injecting drug use, unsafe tattooing, high risk sex, travel to endemic
areas) was the dominant route of transmission in this group.” The researchers
hope their findings will help de-stigmatise HCV infection in the baby boomer
generation and encourage more patients to access testing and potentially
life-saving treatment.
Up to 6 million
individuals in North America are infected with HCV. Approximately
three-quarters of these infections involve patients born between 1945 and 1965,
the baby boomer generation. Previous studies have identified infected blood
products and experimentation with injecting 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 1945-65 birth cohort remains
unclear. A team of investigators therefore analysed 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 five HCV genes to
reconstruct the dynamics of the HCV epidemic in North America.
Analysis of all
five 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.
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,” write 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 Two and its immediate aftermath, a period
when injection and blood transfusion technologies were still in their infancy.
Before 1950,
injecting technology was characterised by the use of glass and metal syringes,
which were sterilised 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 the North America. The period 1920 to 1960 also
saw the expansion of recreational 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 injecting 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 Two…and not only the rise in injecting drug use, which peaked
much later in North America in the late 1960s,” conclude the authors. “The
prevailing view that the North American epidemic is predominately attributable
to past sporadic risky behaviours is not supported by our data.”
The investigators
hope their findings will help reduce the stigma associated with HCV screening,
potentially increasing the number of patients presenting for care and effective
treatment.