Sexually transmitted infections

  • Essentially the presence of any sexually transmitted infection (STI) has been found to increase the risk of becoming infected with HIV.
  • Many STIs also increase HIV viral load and shedding of HIV from the genitals – factors likely to make co-infected people more infectious.
  • Antiviral treatment of genital herpes (HSV-2) has not proven to be an effective strategy for reducing the spread of HIV.
  • Nevertheless, monitoring and treating STIs remains an important priority for sexually active people, both HIV-positive and HIV-negative.

Most sexually transmitted infections (STIs), including herpes simplex 2 (HSV-2), syphilis, gonorrhoea, and chlamydia, are known to increase the risk of HIV infection in HIV-negative persons. STIs also lead to increased shedding of HIV from the genitals of HIV-positive individuals, increasing the risk of transmitting HIV to others.

These risks had already been well established by the 1990s1 2 3 and have since been confirmed by an ever-growing body of research. Notably, the controversial 'Swiss statement' that HIV-positive persons with undetectable viral loads were sexually uninfectious explicitly stated that persons with active STIs were sexually infectious.

While there may be differences in degree of risk attributable to specific, individual STIs, many reviews and analyses treat all STIs, as a group, as risk factors for HIV transmission (e.g., McClelland 20064). A recent UK study, done mostly in MSM, has also found that STIs increased the risk of drug-resistant HIV transmission.5

The main implications are that all sexually active people, both HIV-negative and HIV-positive, should take precautions to avoid STIs, should be regularly screened for infections, and should be promptly treated when necessary. HIV-negative persons with recurrent STIs may be at increased ongoing risk of HIV infection, and should consider extra precautions. In 2005, the UK's Chief Medical Officer recommended that all people seeking treatment for STIs should be offered HIV testing.

People should also be aware that, in some cases (see section on Herpes simplex virus type 2 (HSV-2) below), STIs may continue to increase the risk of HIV transmission, despite treatment of the infection.

There are two main reasons for the effect of STIs on HIV transmission. Firstly, many (although not all) STIs can cause sores or lesions. These so-called ulcerative genital diseases (GUDs) provide a direct physical route of entry for HIV in an uninfected person, and shed high amounts of virus in an infected person, thus making transmission in both directions more likely.

Secondly, immune cells that are, themselves, prone to HIV infection – such as activated T-cells and dendritic cells – are prone to be present in greater numbers at the site of an infection. For instance, herpes simplex virus infection increases the number of activated T-cells and dendritic cells in the cervix, even without ulceration or active HSV shedding.6

Thirdly, STIs can weaken mucosal immunity, making mucous membranes more susceptible to HIV infection.

Many studies have looked at the relationship between STIs and HIV infection; we summarise their key findings here.

Related Links

References

  1. De Vicenzi I et al. A longitudinal study of human immunodeficiency virus transmission by heterosexual partners. NEJM 331(6):341-346, 1994
  2. Hayes RJ et al. The cofactor effect of genital ulcers on the per-exposure risk of HIV transmission in sub-Saharan Africa. J Trop Med Hyg 98:1-8, 1995
  3. Laga M Interactions between STDs and HIV infection. Transcript 28, 1992
  4. McClelland RS and Baeten JM Reducing HIV-1 transmission through prevention strategies targeting HIV-1-seropositive individuals. J Antimicrob Chemo 57:163-166, 2006
  5. Nambiar K et al. Acquisition of transmitted drug resistant HIV-1 infection is associated with the presence of sexually transmitted infections. Fourteenth Conference on Retroviruses and Opportunistic Infections, Los Angeles, abstract 657, 2007
  6. Rebbapragada A et al. Negative mucosal synergy between Herpes simplex type 2 and HIV in the female genital tract. AIDS 21(5): 589-598, 2007
This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.