The HIV epidemic continues to take its greatest toll in sub-Saharan Africa, where more than 60% of the world's 40 million infected persons live [1]. Tanzania, a country with a population of 34.5 million is among the worst affected, having 7% of the adults infected with HIV [2]. There is a diverse pattern of trends in HIV prevalence for different geographical areas in the country. In some areas the reports show a decreased trend in the prevalence and incidence of HIV, especially among individuals aged 15–24 years [3, 4]. In others, there is a gradual and continuing spread of HIV [4, 5]. In all areas however, women continue to experience higher rates of prevalence and incidence than men [2–5], and 58% of the HIV-infected in the whole country are women [6]. There is therefore a need to elucidate risk factors continuing to contribute to the HIV epidemic among women of reproductive age.

In this study we report social, behavioral and biological determinants for HIV, among pregnant women in Moshi urban, Tanzania, including male partner's characteristics and behavior. The study is part of a prospective cohort study that aimed to describe the acceptability of HIV perinatal interventions at the primary health care level as well as to determine factors associated with incident HIV and sexually transmitted infections (STIs) in the postpartum period. The information on determinants for HIV is intended to contribute in improving counseling and in planning for future preventive activities.

Ninety nine percent of the 2664 women counseled agreed to participate. Of the 2654 participating women, 99 agreed to undergo serological testing but declined gynecological examination. The age of the women ranged from 14–43 years (mean, 24.6 years, standard deviation = 5.4 years) and parity from 0–9 (mean, 1.2). Most were married or cohabiting (91%), had completed 7 years of formal education (79%) and were not formally employed (95%). The average income per month was low; 29% had no income and 65% had an income of less than 30,000 Tanzanian shillings or ~ 30 USD per month. The duration of residence in Moshi ranged from less than a year to 42 years (mean, 12.7 years, median, 10 years). Condom use was low; 75% reported they had never used a condom, with only 13% reporting consistent use.

Nearly 7% of the women in the study were HIV-positive, indicating that HIV is still a major public health problem among women of reproductive age in Moshi urban. The prevalence observed (6.9%), is similar to the prevalence of 7.3% described among women aged 15–49 years in Kilimanjaro region, in the recent Tanzania HIV/AIDS Indicator survey [2]. Given the high antenatal attendance rates in the area (>97%), women attending antenatal clinic can be used as a sentinel surveillance population in monitoring trends of HIV infection among adults aged 15–49 years, despite its known limitations [1, 7].

The HIV prevalence was greater among women who started sex at an early age (≤15 years). The prevalence peaked early at 10% among 25–29 year olds [2, 5, 8]. This suggests that most infections in women occur at a younger age, during the first few years after sexual debut [8]. Immature genital tract and cervical ectopy which is common in young women might increase the risk [9, 10]. Untreated STIs may magnify the biological susceptibility [8, 11]. Further, because women tend to have older partners at debut or later, they might be at higher risk because they might be exposed to previously infected partners [8, 12–14]. Preventive programs should therefore target young people, especially women, with the aim to empower them to delay sexual debut and to improve their negotiating skills, especially regarding condom use.

Male factors were strong predictors for HIV. Having a partner who had other women outside the relationship increased the HIV risk by 15-fold. Alcohol use by the partner also increased the HIV risk. The better economic and cultural position of men compared to women in most African settings leads to a skewed balance of power in sexual relationships [12–15]. Men are thus the main decision makers of when and under what circumstances sex will take place [12, 15, 16]. Several reports show that married men report more casual partnerships than married women [8, 12, 13], and when they use alcohol, they have increased risk of unprotected sex and commercial sex [17]. However, due to women's lower social and cultural position than men, women's economic dependence, and domestic violence, most are not in a position to negotiate safe sex [12, 15, 16, 18]. In this study women who gave a history of physical or verbal abuse by the current partner had both an increased risk of HIV and of not coming back for their HIV test results [18, 19]. It is thus vital to design programs that actively involve men in HIV preventive interventions and in other reproductive health issues. The focus of preventive efforts should be to encourage men to use condoms consistently in any sexual encounter with a person of unknown HIV status and reduce the numbers of sexual partners. There is also a need to promote the use of voluntary counseling and testing services as a preventive tool especially for people entering into stable partnerships. Further, culturally sensitive interventions that address domestic violence should be integrated in HIV preventive programs [15, 16, 18].

Women with partners who were mobile (i.e. frequent travelers, or involved in tourism or the mining industry) had a higher HIV prevalence. Mobile men have been shown to report more sexual risk behavior, (e.g. multiple partners, excess alcohol intake and sex with commercial sex workers), putting them and consequently their partners at risk of HIV [20]. It may also be that women with absent partners are more likely to engage in casual partnerships because they are either free, lonely, or experience economic hardship. Recently, a study among couples in Mwanza, Tanzania, showed that there is an increase of sexual risk behavior in both the mobile person and the partner staying behind [21]. Further work is required to assess the vulnerability of this special group of women who are partners of mobile men and preventive efforts extended to both the mobile partners and their women.

A higher HIV prevalence was observed in women who had recently migrated into Moshi (≤2 years). Compared to women who had resided in Moshi for >3 years, they were younger than 25 years (78% vs 49%; p = < 0.001), had no or incomplete primary education (14% vs 10%; p = 0.006), had no income (39% vs 26%; p < 0.001), reported more casual partners in the past 12 months (8.3% vs 4.1%; p = 0.01) and had more GUD (2.6% vs 1.3%; p = 0.04). It may be that most of these women, who had moved to an urban area to seek a better life, had to engage in high risk behavior in order to survive, as shown in South Africa [22]. Mobility and internal migration seems to be an important character of the HIV epidemic in Moshi. Long term programs that will identify migrant women and promote safer sex and economic empowerment are required.

Genital ulcer, active syphilis and HSV-2 were independent risk factors for HIV. STIs increase the efficiency of HIV transmission [11]. Genital ulcers increase the HIV susceptibility by disruption of the mucosa barrier, thus providing an easy port of entry and increase the recruitment and activation of HIV susceptible inflammatory cells. The inflammation and ulceration increases HIV shedding in the genital tract, thus the HIV infectiousness [10, 11]. HSV-2 and syphilis are ulcerative STIs, and are highly prevalent among women in resource poor settings [8, 22–24]. Effective management of STIs reduces the HIV incidence [25], therefore STI control should be prioritized. One strategy for reaching more women will be an integration of STI management in reproductive health clinics. Further, because a growing number of ulcers are caused by HSV-2 [26], its management should be integrated in the GUD syndromic guidelines in Tanzania. Bacterial vaginosis has been shown to be strongly associated with HIV [27]. It is known to be the most common cause of vaginal discharge and consistent correlation between the symptom of vaginal discharge and BV warrants the use of a syndromic approach for timely treatment of this infection [11, 27]. Prompt treatment will reduce not only the risk of HIV transmission, but also the adverse obstetric and gynecological complications associated with BV [11, 27, 28].

Sporadic use of condoms did not confer protection to HIV, similar to what was observed elsewhere [13, 29]. Condoms are effective when used correctly and consistently. Consistent condom use was low among the women. It may also be that people who know or suspect they have HIV may tend to use condoms more to protect their partners. Or condom use may be a marker of high risk sexual behavior as shown in one study, where people with multiple partners reported higher rates of use of condoms than those with a single partner [29].

This study had several limitations. This was a cross-sectional study, so the odds ratios observed may overestimate risk estimates and the associations may not be causal. Secondly, sensitive information regarding the male partner's behavior characteristics was reported by the women. The accuracy may be low due to lack of openness regarding sexual matters between the partners, and probably some degree of guesswork regarding casual partners. Limitation in self-reported data on sexual behavior has been shown, where there is a tendency to under report sexual risk behavior [8, 13]. The results observed in this data may thus be an underestimation of the true association between HIV and behavior characteristics. HIV decreases fertility in women, both from sub fertility and from increased early pregnancy loss [30]. HIV infected women also have higher rates of tubal infertility secondary to pelvic inflammatory diseases [31], therefore the prevalence presented might fail to reflect those who are not able to become pregnant. Lastly, women aged ≥35 years were few (5.3%) in the antenatal clinic, therefore the prevalence might not reflect the picture among women of that age in the community [32].

HIV is still a major health problem among women of reproductive age. The behavior and other characteristics of the male partners in this study were important predictors for HIV in women. Therefore, involvement of men in HIV prevention and in all aspects of reproductive health programs is of the utmost importance if we want to make advances in preventing HIV in women and in the community at large. Empowering women with the skills and rights to negotiate in sexual matters must be more successfully addressed. Other important preventive strategies should aim at control of STIs, reduction of number of partners, increased use of condoms in long term partnerships, responsible alcohol use and targeting mobile people.