Sexually transmitted infections greatly increase the risk of HIV infection in pregnancy

Pregnant women in Kenya have a similar risk of HIV infection during pregnancy to serodiscordant couples or sex workers, Dr John Kinuthia told the 21st Conference on Retroviruses and Opportunistic Infections (CROI) in Boston last week.

In this prospective cohort study of pregnant and postpartum women in western Kenya, conducted between May 2011 and June 2013, 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 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.

Women with a history of sexually transmitted infections (STIs) had close to a four-fold increased risk of acute HIV infection (OR = 3.8, 95% CI: 1.4-10.6) while being having syphilis or bacterial vaginosis at enrolment had a ten- and close to three-fold increased risk, respectively (OR = 10, 95% CI: 2.00-46.0 and OR = 2.6, 95% CI: 1.2-5.8). These findings underscore the importance of screening for and treatment of STIs in HIV prevention, Dr Kinuthia added.

While much remains to be done – an estimated 35% 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 5%; without any intervention, transmission rates would range between 25 and 40%.

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 1 to 3 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 routine immunisation visits.

Of the 4245 women seeking care at Ahero and Bondo district hospitals, where HIV prevalence at antenatal care clinics is 22 and 26%, respectively, 3408 were negative and, of the 2351 eligible, 1304 (56%) enrolled in the study.

Women had a median age of 22 (interquartile range [IQR]: 19 to 26) and 78% (1022) of the women were married, for a median time of 4 years (IQR: 1 to 8). Seven per cent (87) reported a history of STIs. One per cent of the women knew their partner was HIV positive while 34% (445) did not know their partner’s status.

Twenty-four women had newly identified HIV infection giving an overall HIV incidence rate of 2.34/100 person-years, (95% CI: 0.56-4.34).   

Of these, 10 had a positive NAAT at enrolment (five categorised as seroconversion and five as acute infection). Fourteen acquired HIV during follow-up; two late in the pregnancy (week 32), three at 14 weeks postpartum and seven at nine months postpartum.

Of the women with acute infection, none reported an HIV-positive partner. It is not uncommon for a man to test by proxy; if a woman tests negative at antenatal care, the partner assumes he is also negative, said Dr Kinuthia. The partner’s status was not confirmed. Being married for a shorter period of time (OR = 1.14, 95% CI: 1.01-1.35) was also associated with increased risk for acute HIV infection.

Among 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.