Viral load in the blood and rectal secretions of
HIV-positive gay men are highly correlated, according to US research published
in the September 1st edition of the Journal of Infectious Diseases. The study also showed that the
presence of sexually transmitted infections did not increase rectal viral load.
Individuals with a plasma viral load above 1000 copies/ml
were significantly more likely to have detectable virus in the rectum.
“Our data add substantially to the few published studies of
HIV shedding in rectal secretions of MSM [men who have sex with men],” comment
the investigators, “we were able to quantify HIV RNA in rectal secretions,
demonstrate the linear correlation between increasing plasma load and rectal
viral load and determine a threshold plasma viral load that distinguished
detectable from undetectable rectal viral load.”
They also believe that their findings have important
implications for current debates about the use of HIV treatment as prevention,
commenting: “Combination antiretroviral therapy will have a similar effect on
reducing HIV transmission in MSM, as seen in studies of heterosexual discordant
Gay men remain one of the groups most affected by HIV.
Unprotected anal sex is the primary mode of HIV transmission for gay men, and it
is estimated that 28% of infections in this population are due to insertive
anal intercourse. Therefore,
rectal secretions are an important potential source of HIV transmission.
Moreover, gay men have a high incidence of bacterial
sexually transmitted infections, and these have been shown to increase urethral
HIV viral load.
However, the relationship between plasma and rectal viral
load is poorly understood. Nor is the impact of sexually transmitted
infections on rectal viral load well established.
Therefore investigators from the Study to Understand the
Natural History of HIV in the Era of Effective Therapy (the “SUN” study)
measured rectal viral load using samples collected via swabs used to monitor
patients for infection with gonorrhoea or chlamydia. The investigators paired
rectal and plasma measurements of viral load.
The study involved 80 men, and 59 (74%) were taking
antiretroviral therapy. The patients’ median CD4 cell count was 467 cells/mm3
and 63% had a plasma viral load below 1000 copies/ml.
Almost all the men (95%) had rectal human papilloma virus
(HPV) infection, and two-thirds had herpes simplex virus. Rectal gonorrhoea or
chlamydia was detected in 39% of men.
Rectal HIV was detected in 38% of men overall and in 42% of
Viral load in rectal samples and plasma were highly
correlated. This included men with rectal sexually transmitted infections.
HIV was significantly less likely to be detected in the
rectal samples of men who had a plasma viral load below 1000 copies compared to men
with a blood viral load above that value (p < 0.001).
A lower CD4 cell count (p < 0.001) was also associated
with detectable virus in the rectum, as was not taking HIV therapy (p <
However, after controlling for potential confounders, the
investigators found that the only factor associated with an increased risk of
having detectable virus in the rectum was a plasma viral load above 1000
copies/ml (p = 0.008).
“We believe our findings demonstrate that among MSM
receiving contemporary antiretroviral therapy, controlling plasma viral load is
an important means (in fact, perhaps the most important) of reducing rectal
viral load, underscoring the value of expanded use of early cART among
HIV-infected MSM in the United States to reduce HIV transmission from exposure
to rectal secretions,” comment the investigators.
The researchers also believe that taking HIV therapy “may
mitigate the effect of STIs on HIV transmission from infected MSM to their
They conclude “our findings indicate that a low plasma HIV
viral load is associated with a low HIV load in rectal secretions…these
findings support the use of cART as an effective means of reducing HIV
transmission among MSM in the United States by reducing the amount of virus
shed in body sites where transmission occurs.”