Plasma and rectal viral load correlated in HIV-positive gay men: supports use of treatment as prevention

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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.”



The last part of the large intestine just above the anus.


The fluid portion of the blood.

detectable viral load

When viral load is detectable, this indicates that HIV is replicating in the body. If the person is taking HIV treatment but their viral load is detectable, the treatment is not working properly. There may still be a risk of HIV transmission to sexual partners.


Chlamydia is a common sexually transmitted infection, caused by bacteria called Chlamydia trachomatis. Women can get chlamydia in the cervix, rectum, or throat. Men can get chlamydia in the urethra (inside the penis), rectum, or throat. Chlamydia is treated with antibiotics.

ribonucleic acid (RNA)

The chemical structure that carries genetic instructions for protein synthesis. Although DNA is the primary genetic material of cells, RNA is the genetic material for some viruses like HIV.


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 couples.”

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 rectal samples.

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 < 0.001).

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 uninfected partners.”

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.”


Kelley CF et al. HIV-1 RNA rectal shedding is reduced in men with low plasma HIV-1 RNA viral loads and is not enhanced by sexually transmitted infections in the rectum. J Infect Dis 204: 761-67, 2011 (click here for the free abstract).