Although several explanations have been proposed, exactly how and why STDs have this effect has not been clear. Now, Teunis B.H. Geijtenbeek and colleagues, at VU University Medical Center, The Netherlands, have described a way in which STDs can increase acquisition of HIV-1 infection in an ex vivo human skin explant model that they hope might be amenable to therapeutic modulation to prevent HIV transmission. In the ex vivo human skin explant model, although immature immune cells known as Langerhans cells (LCs) captured HIV, they did not efficiently transmit the virus to T cells, something that is essential for the initiation of full disease. By contrast, efficient virus transmission was observed if LCs were activated by inflammatory stimuli. As the infectious agents that cause the STDs thrush and gonorrhea triggered the same inflammatory stimuli in vaginal and skin explants, the authors suggest that in the presence of an STD-causing infectious agent, LCs might become activated, thereby increasing an individual’s risk of becoming infected with HIV.
In this prospective cohort study of pregnant and postpartum women in western Kenya, conducted between May and June , more than half of all incident HIV infections diagnosed were acute infections detected during pregnancy. The remaining incident infections were detected shortly after study recruitment and were estimated to have occurred prior to study entry. These findings reinforce the need for repeat HIV testing during pregnancy post exposure prophylaxis and underscore the need to use more sensitive methods including pooled nucleic acid amplification tests (NAAT) especially in regions with high HIV prevalence and incidence, Dr Kinuthia noted. While much remains to be done – an estimated of pregnant women in low- and middle-income countries get an HIV test – considerable progress has been made in the identification and treatment of women with HIV in prevention of mother-to-child transmission (PMTCT) programmes.
The availability of effective antiretroviral treatment for PMTCT and expansion of ART and access to PMTCT services in many countries in sub-Saharan Africa has resulted in significant declines in transmission rates. For example, Botswana and South Africa have reduced transmission rates to below ; without any intervention, transmission rates would range between However, while women with chronic HIV infection are the primary target of PMTCT programmes, the need to ensure pregnant women who do not have HIV do not acquire it is of no less importance in the prevention of adult infection and vertical transmission. Women in the window period or those who acquire HIV after HIV testing will often go unrecognised and untreated. Women with acute HIV infection have higher viral loads, putting them at increased risk of passing the virus on to their infants, especially if they are not taking antiretrovirals. Within this context, the researchers chose to look at the rates and co-factors linked to acute HIV infection among pregnant and postpartum women.
Pregnant women testing HIV negative, following two rapid HIV tests, at their antenatal visit or within the previous three months were enrolled after consenting. They completed questionnaires on sexual behaviour and socio-demographic characteristics. Blood was taken for nucleic acid testing and run in pools of ten samples. Those who tested negative had tests every months throughout the nine-month postpartum follow-up. Genital swabs were collected for STI detection at baseline and throughout follow-up. Postnatal visits for the most part mirrored routineAmong women with and without HIV, maternal age, marital status, age difference from the partner, and infection with other STIs did not differ. Dr Kinuthia stressed the need to prioritise strategies to detect and treat STIs.
Other HIV prevention options should be aggressively promoted, he added, including PrEP, microbicides and promotion of partner HIV testing and treatment. While this innovative study design provides stronger evidence of the possible causal role of STI in incident HIV infection, prospective studies are required to show temporal relationships more definitively. Several important cohort studies have recently been reported and all are consistent in showing an increased risk of HIV in people with STI, but the size of the risk and the importance of the particular pathogens varies by population. Two prospective studies of MSM in the USA also showed an important increase in HIV incidence associated with STI. One cohort study found that repeated recent rectal infection with gonorrhoea or Chlamydia increased the risk of HIV more than 8-fold after controlling for known and measured confounders. Menza and colleagues developed a risk score model for HIV acquisition among MSM based on a longitudinal study, in which a history or current bacterial STI was one of the strongest predictors for HIV acquisition. A community based cohort of MSM in Australia also found rectal infections to be associated with incident HIV, with both gonorrhoea and anal warts significantly associated after controlling for risky behaviour.Finally, in an extensive systematic review and meta-analysis, Boilly and colleagues summarised data from study populations to estimate the risk of HIV transmission per act in heterosexuals. They found that current or past genital ulcers in the HIV susceptible partner increased per-act infectivity five-fold compared with no STI.