HIV superinfection appears to be extremely rare, a Dutch
study published in the June 1st edition of the Journal of Infectious Diseases suggests.
The study is one of the few attempts to use ongoing virological monitoring and behavioural data to establish the likely incidence of superinfection, albeit in a small cohort, and points to the neglect of a question that remains important for giving advice on HIV prevention strategies that might encourage the practice of serosorting - sex with partners of the same HIV status.
Researchers monitored 15 HIV-positive gay men for evidence of
superinfection for an average of almost six years. All the men either reported
unprotected anal sex, or had a history of sexually transmitted infections. Despite
this risk, no cases of superinfection were detected.
“With no putative case of HIV-1 superinfection detected in
15 individuals over a total of 88.3 PY [person years], we observed a low incidence
rate of HIV-1 superinfection (incidence rate: 0 per 100 PY, 95% CI: 0- -4.2),”
write the investigators.
However, they do not regard their results as definitive and
call for further research into this matter. In particular, they speculate that
the level of risk of the men in their study may not have been high enough to
lead to superinfection.
Intensive case finding has identified approximately 50 cases
of confirmed HIV superinfection (infection with a second strain of the virus).
Some investigators have speculated that the phenomenon may
be much more common than this figure suggests.
To try and establish a better understanding of this
controversial subject, investigators from the Netherlands studied blood samples
obtained from 15 HIV-positive gay men recruited to the Amsterdam Cohort Study
between 1986 and 1997.
Blood samples were obtained from these men every three
months, and at six-monthly intervals they were interviewed about their sexual
behaviour. All the men reported unprotected anal sex with at least two partners
in one or more six-month period, and/or infection with syphilis or gonorrhoea.
Phylogenetic analysis was used to see if any of the men had
been superinfected with another strain of HIV.
Of note, the study was conducted using samples obtained in
the era before effective antiretroviral therapy became available.
Superinfection among individuals treated with HIV therapy appears to be
A total of five individuals reported four six-month periods
of risk; five patients reported three periods of risk; and the remaining five
individuals reported one or two risk periods.
Overall, the men contributed over 88 person years of
follow-up, an average of 5.8 years per patient.
Intensive phylogenetic analysis failed to detect a single
case of superinfection.
“While we had expected to increase the odds of detecting
HIV-1 superinfection in this study by studying longitudinal samples covering
time periods of unsafe sexual risk behaviour, no cases of superinfection were
detected,” write the authors.
However, they note that they may not have been able to
detect minority populations of superinfecting virus, or transient
Even though the patients enrolled in their study reported
risky sex, the investigators suggest that this may not have been at a
sufficient level to lead to superinfection. They note that HIV-positive African
sex workers who were superinfected reported “a 10-fold to 30-fold higher number
of sexual partners than homosexual men in our cohort.”
The investigators conclude that their analysis “resulted in
absent detection of HIV-1 superinfection and hence a low incidence of HIV-1
superinfection in this study may point to external risk and/or host factors
involved in acquisition of HIV-1 superinfection.”
They suggest that “additional longitudinal studies are
needed to estimate the impact of each factor that may increase the risk for
establish of HIV-superinfection.”
However, conducting such studies may be difficult in settings where men could be criminalised either for HIV transmission or for non-disclosure of HIV status. Men may be disinclined to provide frank information about their sexual behaviour in such settings, even where the object of inquiry is sex with partners of the same HIV status.