Sexually transmitted infections (STIs) are a major public health problem, especially in developing countries 12. They are highly prevalent among pregnant women in Africa and cause significant maternal and perinatal morbidity 23456. STIs and other reproductive tract infections (RTIs) have been associated with a number of adverse pregnancy outcomes including abortion, stillbirth, preterm delivery, low birth weight, postpartum sepsis, neonatal pneumonia, neonatal blindness & congenital infection 1234. In addition, STIs/RTIs have been shown to facilitate transmission of HIV 789101112. The control of STIs/RTIs, especially in pregnancy, is thus a priority, particularly in resource-poor settings where they are prevalent.

The prevalence of STIs however, has been shown to vary from one country to another and among different groups within the same country 2. In Tanzania, the difference of STI/RTI prevalence by region, population and time-period has been observed 36131415161718. There is thus a need to have local knowledge of the epidemiology of STIs/RTIs by periodically monitoring the prevalence of etiological agents. This information is useful in guiding clinical management, treatment protocols and to form the basis for STI surveillance. In this paper we report the prevalence of STIs/RTIs among pregnant women attending routine antenatal care in Moshi urban, Tanzania, as well as comparing the occurrence of infections among HIV-seropositive and sero-negative women. In addition, we compared the results of this study with previous published data on the prevalence of sexually transmitted infections among pregnant women in the same clinics.

To simplify the reading of the text, the acronym RTIs is used exclusively and is to be understood to include STIs as well as other non sexually transmitted diseases of the reproductive tract (i.e. bacterial vaginosis and candidiasis).

The age of the 2654 participating women ranged from 14–43 years (median 24 years), parity from 0–9 (median 1) and gestation age from 28–40 weeks (median 30 weeks). Other demographic details are described in Table 1.

The prevalence of laboratory diagnosed RTIs by HIV status is shown in Table 2. Seven percent of the women had HIV infection, 0.9% had active syphilis, 33.6% were HSV-2 positive and 17.5% had IgG antibodies for C trachomatis. The prevalence of N gonorrhoeae was low (0.5%) while 23.9% of the women had trichomoniasis and/or bacterial vaginosis.

Except for candidiasis, the prevalence of both viral and bacterial RTIs were higher in HIV-seropositive women than in the HIV-seronegative women, significantly for syphilis (p < 0.001), HSV-2 (p = 0.03), gonorrhoea (p = 0.05), Chlamydia trachomatis Ab (p = 0.004), bacterial vaginosis (p < 0.001) and genital ulcers (p = 0.002), Table 2.

Table 3 shows a comparison of RTI prevalence among pregnant women with published work which was carried out in 1999 at the same clinics as the current study 18. A significant decline in curable RTIs was observed, especially for syphilis (from 3.4% to 0.9%; p = 0.001), trichomoniasis (from 23.4% to 5.0%; p < 0.001) and bacterial vaginosis (from 31.4% to 20.9%; p = 0.001). No significant decrease was observed in the prevalence of HSV-2 infection.

In this study viral infections (HSV-2 and HIV) are more common than the curable non-viral STIs like trichomoniasis, syphilis or gonorrhoea 141617. We also noted a decline of curable genital tract infections among pregnant women between 1999 and 2004. A high prevalence of HSV-2 and decreasing prevalence of curable genital tract infections like syphilis, chlamydia, gonorrhoea, trichomoniasis and bacterial vaginosis has been reported in several sub-Saharan countries among pregnant women 152223, among women in the general population 23, and among women in high risk groups 161723. The introduction of and scaling up of syndromic approach for management of STIs in most primary health clinics may partly explain the decrease 623. The change in the genital infection spectrum however, highlights the need to strengthen STI surveillance, so as to be able to adjust syndromic management protocols according to the epidemiological situation.

Despite the declining trend, the prevalence of trichomoniasis (5%) and bacterial vaginosis (20.9%) are still high, considering that this was a pregnant population. Untreated, trichomoniasis (TV) has been associated with preterm birth and low birth weight (LBW), while bacterial vaginosis (BV) can cause preterm rupture of membranes, preterm birth, LBW and postpartum sepsis especially in women with a previous history of preterm delivery 2. Prematurity and low birth weight are among the leading causes of perinatal morbidity and mortality in resource-poor settings 1210. Studies have also indicated that both BV and TV may increase the risk of HIV acquisition, and BV may have an effect on mother-to-child transmission of HIV 101112. Efforts are thus required to treat these vaginal infections in pregnancy. An approach like presumptive treatment (mass treatment on the presumption that the disease might be present) has been associated with significant reduction in the prevalence of these infections, and in the incidence of LBW, early neonatal death and preterm delivery 4.

The active syphilis prevalence of 0.9% was similar to that reported for women in the general population (0.2%) or among bar workers (1.1%) in the same district 1417. However it was lower than in pregnant women in the Mwanza (7.7%), Mbeya (4.1%) and Kagera (14.9%) regions in Tanzania, and among pregnant women in Uganda (3.3%), Zimbabwe (3.4%), Mozambique (4.7%) and Cameroon (13%), showing variation within and between countries in Africa 3456152224. Our results however might be an underestimation in the prevalence of syphilis because women with early foetal loss resulting from syphilis would not be represented, since we recruited women in the third trimester 3. Lumbiganon et al (2002) showed that even with a low background prevalence of 0.9%, women with syphilis had significantly more adverse pregnancy outcomes e.g. LBW and perinatal death 25. Syphilis screening and treatment in pregnancy is thus cost-effective even at prevalences < 1% and supports the WHO recommendation to perform serological screening on all pregnant women at first visit 1. With resources being mobilized for expansion of prevention of mother-to-child transmission of HIV programs in most sub-Saharan African countries, this opportunity should be used to expand syphilis screening and treatment at the same time.

The higher prevalence of STIs and bacterial vaginosis among HIV-seropositive women than seronegative women has also been reported among pregnant women in Zimbabwe, Cameroon, Thailand and USA 5824. HIV-infected people have higher rates of genital infection probably because of shared behavioral risk factors that facilitate transmission of both infections 7, or increased susceptibility to some RTIs like gonorrhoea and GUD, especially with advanced immune suppression 26. RTIs in HIV-infected women has been associated with more severe adverse reproductive health outcomes than in uninfected women, including pelvic inflammatory disease, high grade cervical intraepithelial lesions, postpartum endometrititis, preterm birth and neonatal death 22425. Also, the presence of bacterial vaginosis, candidiasis, trichomoniasis, gonorrhoeae, chlamydia and HSV-2 in HIV-infected women, increases HIV genital shedding, thus an increased concentration of HIV in genital secretions 9102829. Increased infectiousness increases the risk of both vertical and sexual HIV transmission. In fact, studies have recently shown that bacterial vaginosis, chorioamnionitis, genital ulcers and HSV-2 are associated with increased rates of mother-to-child HIV transmission 8103031. Efforts to expand HIV-counseling and testing services to all centers offering antenatal care is vital in order to identify HIV-infected women. Apart from offering antiretroviral therapy (ART) to reduce perinatal HIV transmission, the women should also be offered screening for genital tract infections. Treatment of genital infection significantly lowers genital HIV concentrations 9102829, thus treatment of maternal genital infections in HIV-infected women during pregnancy may substantially reduce negative reproductive effects on the women themselves, may reduce sexual HIV transmission and play a part in reducing mother-to-child transmission. Efforts to address RTIs in HIV-infected women should not be limited to pregnancy but should also be extended to ART care clinics.

There may be possible limitations in the study regarding some of the laboratory tests used to diagnose RTIs. Culture and microscopy were used to diagnose gonorrhoeae and trichomoniasis in this study. Nucleic acid amplification technology using polymerase chain reaction (PCR) has been shown to have a higher sensitivity and specificity than culture and microscopy for identification of both gonorrhoea and trichomoniasis 3233. The traditional tests used might have thus missed a substantial proportion of these infections. Further, we used an IgG antibody test to diagnose Chlamydia trachomatis. This test can only show the proportion of women who had been exposed to the Chlamydia infection in the past. It cannot differentiate between women with active and with past infections. Therefore it may be used only for epidemiological studies and not for diagnosing women for treatment.

Despite the possible limitations, the study has demonstrated that STIs and other reproductive tract infections are still prevalent among pregnant women in the area. Routine screening and treatment during antenatal care is recommended. HIV-infected women should receive adequate screening for genital tract infections during pregnancy. Future research and public health preventive efforts should target not only the classical bacterial RTIs but also HSV-2 as it was the most prevalent STI. Lastly, studies using more sensitive assays (PCR) for screening STIs during pregnancy are required, in order to give a more precise picture of STI occurrence.

The authors declare that they have no competing interests.

SEM designed the study, recruitment of participants, collected and entered data, analyzed data and drafted the manuscript. JU participated in data collection, laboratory testing and data analysis, revising the drafted manuscript. AH conception, design, analysis and reviewed the drafted manuscript. EM designed the study, participated in analysis and interpretation, reviewed the drafted manuscript. SJ design of laboratory testing, chlamydia testing, interpretation of results. NES designed the study, supervised laboratory testing, reviewed the drafted manuscript. BSP conception, design, coordinated the study, interpreted data and reviewed the drafted manuscript. All authors read and approved the manuscript.