Chlamydia and gonorrhea may drive as much as 10 percent of HIV transmissions among men who have sex with men (MSM). Contracting either of these two bacterial sexually transmitted infections (STIs) can raise the transmissibility of HIV among those who have untreated HIV and therefore a detectable viral load. Additionally, chlaymdia or gonorrhea infection can make those who do not have HIV more susceptible to contracting it.

STIs have risen steeply in the United States in recent years, in particular among MSM.

Publishing their findings in Sexually Transmitted Diseases, researchers used mathematical modeling to project chlamydia and gonorrhea’s combined contributions to HIV transmissions over a 10-year period. Specifically, they looked at one scenario in which the two STIs raised the risk of transmission and acquisition of HIV and compared that scenario with a second one in which gonorrhea and chlamydia did not affect the HIV incidence rate.

The probability of HIV transmission, according to the mathematical model, was modified not just by gonorrhea and chlamydia but also by the viral load of the HIV-positive sexual partners, the presence of the CCR5 delta-32 mutation that confers genetic resistance to the virus, condom use, sexual role (insertive or top versus receptive or bottom) and whether the insertive partner was circumcised.

Male circumcision is associated with about a 60 percent reduced risk of female-to-male transmission of HIV. At least in theory, circumcision may also reduce the risk of transmission of HIV when the receptive partner in sex between men has the virus and the insertive partner is HIV negative; no study has proved this, however.

For HIV-positive partners not taking antiretrovirals, the study authors considered viral load as a continuous function of time since infection and disease stage.

Gonorrhea and chlamydia infection were considered active until diagnosis and antibiotic treatment or the body’s natural clearance of the STIs, which takes place after an average 246 and 310 days, respectively.

At the outset of the 10-year theoretical period, the prevalence of HIV was 14.7 percent while 1.3 percent of the population of MSM had gonorrhea and 3.7 percent had chlamydia.

Overall, 10.4 percent of the new HIV infections, the researchers concluded, would be driven by chlamydia and gonorrhea.

“With [sexually transmitted diseases] increasing year after year and investment in prevention lagging, our field is in crisis,” David C. Harvey, executive director of the National Coalition of STD Directors, said in a press release. “It’s time to mobilize as a nation to address the STD epidemic, and this study gives us our marching orders. Our organizations welcome and fully endorse the findings of this expert panel.”

“The historic levels of STDs imperil our progress towards ending HIV,” Harvey continued. “We can’t hope to end HIV without also addressing STDs.”


NCSD is pushing Congress to grant an additional $70 millionfor the Centers for Disease Control and Prevention’s (CDC) STI prevention program to respond to the recent surge in transmissions of chlamydia, gonorrhea and also syphilis. The program’s current $157.3 millionannual budget reflects a 40 percent decline in purchasing power since 2003, according to NCSD.

To read the study, click here.