HIV and hepatitis
C virus (HCV) transmission networks are closely linked, according to Swiss
research published in the International
Journal of Epidemiology. Combining clinical data with phylogenetic analysis
of HIV samples from a drug resistance database showed that the risk of incident
HCV infection was increased by a factor of two if a patient was “clustered”
with another patient with HCV.
indicate that the transmission networks of HIV and HCV are correlated and overlap
even beyond the degree that can be expected by demographic variables such as
risk group…geography, sex and age,” comment the authors. “Thus, our analysis
shows that the location of an HIV-infected patient on the HIV phylogeny can
serve as an indicator for the risk of an HCV coinfection.” They believe their
findings have important implications for HCV prevention efforts, allowing the
identification of people with an especially high risk of infection.
HIV and HCV can
both be acquired by contact with blood. There is also an ongoing epidemic of
sexually transmitted HCV among HIV-positive gay men. A significant proportion
of people living with HIV therefore have hepatitis C co-infection, and liver disease
is an important cause of serious illness and death in this group.
extent to which HIV and HCV transmission networks overlap is uncertain. A
clearer understanding of this issue could assist in the development of
targeted HCV prevention campaigns.
obtained information on HCV infection status for people enrolled in the Swiss
HIV Cohort Study (SHCS). This was combined with information on HIV and HCV risk
group – injecting drug use (IDU), heterosexual, men who have sex with men
(MSM), heterosexual/IDU, or MSM/IDU. The investigators then examined 15,000
blood samples obtained from 10,000 people in the SHCS HIV drug resistance
database. A technique called phylogenetic analysis allowed them to construct
HIV transmission pairs. Linking clinical and phylogenetic data enabled the
investigators to examine the interaction between the spread of HIV and HCV.
A total of 2768 people (28%) had at least one positive HCV test and were classified as having
prevalent HCV infection. A further 208 individuals (2%) had a first negative HCV
test and a subsequent positive result. These patients were classified as having
incident HCV infection.
differed according to risk group. It was highest among injecting drug users
(95%), heterosexual/IDU (72%) and MSM/IDU (27%), but much lower in MSM (5%) and
analysis was restricted to the 7644 people in the drug resistance database
with HIV subtype-B infection. A total of 1555 possible HIV transmission pairs
were identified in which the HCV status was known for both members. In 907 of
these pairs both members were HCV-negative; in 303 one member was HCV-infected
and in 345 both were HCV-positive.
The risk of HCV
co-infection was significantly increased if the other patient in the pair had
HCV co-infection as well (OR = 13.6; 95% CI, 10.5-17.6). This extremely high
risk was due to the clustering of IDUs with other IDUs.
association between the HCV status of individuals in transmission pairs
persisted when risk groups were considered separately.
for factors including sex, age and transmission group, the authors found that people in HIV transmission pairs were much more likely to be HCV infected if
their partner in the pair was also HCV-positive (OR = 3.2; 95% CI, 2.2-4.7).
“We observed a
strong clustering of prevalent HCV cases on the HIV phylogeny even after
controlling for the most important demographic confounders,” comment the
HCV-negative individuals were more likely to become infected with HCV if
they belonged to a transmission pair where their partner was HCV-positive (HR =
2.1; 95% CI, 1.1-3.8). This finding persisted when the investigators restricted
their analysis to incident HCV infections in MSM (HR = 2.29; 95% CI, 0.9-5.4).
write the authors, “that the observed doubling of HCV incidence in individuals
clustering with HCV-coinfected partners on the HIV phylogeny was, at least in
part, mediated through sexual transmission of HCV.”
They conclude that
people whose HIV is closely related to a patient co-infected with HCV have a
higher risk of becoming infected with HCV. These patients “could constitute
target groups where intensified testing and counselling are particularly