Research Article: Field evaluation of SD BIOLINE HIV/Syphilis Duo assay among pregnant women attending routine antenatal care in Juba, South Sudan

Date Published: October 10, 2018

Publisher: Public Library of Science

Author(s): Dennis K. Lodiongo, Bior K. Bior, Gregory W. Dumo, Joel S. Katoro, Juma J. H. Mogga, Michael L. Lokore, Abe G. Abias, Jane Y. Carter, Lul L. Deng, Yap Boum.


The SD BIOLINE HIV/Syphilis Duo assay is the first World Health Organization prequalified dual rapid diagnostic test for simultaneous detection of HIV and Treponema pallidum antibodies in human blood. Prior to introducing the test into antenatal clinics across South Sudan, a field evaluation of its clinical performance in diagnosing both HIV and syphilis in pregnant women was conducted. SD Bioline test performance on venous blood samples was compared with (i) Vironostika HIV1/2 Uniform II Ag/Ab reference standard and Alere Determine HIV 1/2 non-reference standard for HIV diagnosis, and (ii) Treponema pallidum hemagglutination reference standard and Rapid plasma reagin non-reference standard for syphilis. Sensitivity, specificity, positive predictive value (PPN), negative predictive value (NPV) and kappa (κ) value were calculated for each component against the reference standards within 95% confidence intervals (CIs); agreements between Determine HIV 1/2 and SD Bioline HIV tests were also calculated. Of 442 pregnant women recruited, eight (1.8%) were HIV positive, 22 (5.0%) had evidence of syphilis exposure; 14 (3.2%) had active infection. For HIV diagnosis, the sensitivity, specificity, PPV and NPV were 100% (95% CI: 63.1–100), 100% (95% CI: 99.2–100), 100% (95% CI: 63.1–100) and 100% (95% CI: 99.2–100) respectively with κ value of 1 (95% CI: 0.992–1.000). Overall agreement of the Duo HIV component and Determine test was 99.1% (95% CI: 0.977–0.998) with 66.7% (95% CI: 34.9–90.1) positive and 100% (95% CI: 0.992–1.000) negative percent agreements. For syphilis, the Duo assay sensitivity was 86.4% (95% CI: 65.1–97.1) and specificity 100% (95% CI: 99.1–100) with PPV 100% (95% CI: 82.4–100), NPV 99.2% (95% CI: 97.9–99.9) and κ value 0.92 (95% CI: 0.980–0.999). Our findings suggest the SD Bioline HIV/Syphilis Duo Assay could be suitable for HIV and syphilis testing in women attending antenatal services across South Sudan. Women with positive syphilis results should receive treatment immediately, whereas HIV positive women should undergo confirmatory testing following national HIV testing guidelines.

Partial Text

Globally, an estimated one million syphilis infections [1] and 1.5 million human immunodeficiency virus (HIV) infections [2] occur in pregnant women annually. Approximately 30% of pregnant women with untreated syphilis will have stillbirths or neonatal death, and another 30% will deliver babies with congenital syphilis, a condition with a mortality of up to 50% [3]. Syphilis infection during pregnancy also increases the risk of mother-to-child transmission (MTCT) of HIV [4]. Syphilis infection in adults causes epithelial and mucosal breaches facilitating sexual transmission of HIV virions. In addition, Treponema pallidum (T. pallidum) and its pro-inflammatory components induce expression of chemokine receptor type 5 (CCR5) on human monocytes, thereby enhancing the susceptibility of these cells to HIV infection [5]. Early screening and effective treatment of syphilis cures syphilis in pregnancy and prevents congenital syphilis and neonatal deaths [6]. Integrating rapid syphilis testing into national HIV programmes in South Sudan would prevent an estimated 1,125 congenital syphilis cases and 1,223 stillbirths and neonatal deaths annually, with a potential cost saving of 525,000 USD [7]. Timely HIV diagnosis in pregnant women is crucial for effective prevention of MTCT and optimal clinical management of HIV [2]. Screening for HIV and syphilis in pregnant women is recommended by the World Health Organization (WHO) to reduce the morbidity and mortality associated with these undiagnosed and untreated infections [8].

Four hundred and forty two (442) venous blood specimens were collected from pregnant women, and tested and analysed between June and August 2016. Eight (1.8%) of 442 pregnant women were HIV positive, 22 (5.0%) had evidence of syphilis exposure while 14 (3.2%) of these were active infections. These results together with the sensitivity and specificity of the SD Bioline Duo test are shown in Table 1.

The present data showed overall good clinical performance of the SD BIOLINE HIV/Syphilis Duo RDT for detection of both HIV and syphilis antibodies in pregnant women attending routine antenatal services in Juba, South Sudan. Eight participants were confirmed HIV positive while 22 had evidence of syphilis antibodies with 14 active infections. No participant was co-infected. All HIV and syphilis confirmed cases were managed by each facility following standard protocols.

The SD BIOLINE HIV/syphilis Duo RDT showed good clinical field performance with venous blood specimens from pregnant women attending antenatal clinics in Juba, South Sudan; having almost perfect concordance with the reference standards. The Duo RDT performed better for HIV than for syphilis diagnosis. It also performed better than the Determine HIV 1/2 screening test in terms of ruling out an HIV infection. This RDT kit offers an opportunity for simultaneous screening of both HIV and syphilis in pregnant women across our antenatal care and prevention of mother to child transmission (PMTCT) programs. However, for country wide rollout, a performance evaluation of the South Sudan National HIV test algorithm with a consideration of the SD BIOLINE HIV/syphilis Duo RDT as a first test is recommended.




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