Comparison of the diagnostic accuracy of a rapid immunochromatographic test and the rapid plasma reagin test for antenatal syphilis screening in Mozambique Pablo J Montoya,a Sheila A Lukehart,b Paula E Brentlinger,c Ana J Blanco,a Florencia Floriano,a Josefa Sairosse,d & Stephen Gloyd c Objective Programmes to control syphilis in developing countries are hampered by a lack of laboratory services, delayed diagnosis, and doubts about current screening methods. We aimed to compare the diagnostic accuracy of an immunochromatographic strip (ICS) test and the rapid plasma reagin (RPR) test with the combined gold standard (RPR, Treponema pallidum haemagglutination assay and direct immunofluorescence stain done at a reference laboratory) for the detection of syphilis in pregnancy. Methods We included test results from 4789 women attending their first antenatal visit at one of six health facilities in Sofala Province, central Mozambique. We compared diagnostic accuracy (sensitivity, specificity, and positive and negative predictive values) of ICS and RPR done at the health facilities and ICS performed at the reference laboratory. We also made subgroup comparisons by human immunodeficiency virus (HIV) and malaria status. Findings For active syphilis, the sensitivity of the ICS was 95.3% at the reference laboratory, and 84.1% at the health facility. The sensitivity of the RPR at the health facility was 70.7%. Specificity and positive and negative predictive values showed a similar pattern. The ICS outperformed RPR in all comparisons (P<0.001). Conclusion The diagnostic accuracy of the ICS compared favourably with that of the gold standard. The use of the ICS in Mozambique and similar settings may improve the diagnosis of syphilis in health facilities, both with and without laboratories. Keywords Syphilis serodiagnosis; Prenatal diagnosis; Mozambique (source: MeSH, NLM). Mots clés Séro-diagnostic syphilis; Diagnostic prénatal; Mozambique (source: MeSH, INSERM). Palabras clave Serodiagnóstico de la sífilis; Diagnóstico prenatal; Mozambique (fuente: DeCS, BIREME). Arabic Bulletin of the World Health Organization 2006;84:97-104. Voir page 103 le résumé en français. En la página 103 figura un resumen en español. Introduction cost-effective as a means to reduce fetal and treatment have hampered efforts to and infant morbidity and mortality,13 prevent congenital syphilis in Mozam- Syphilis is an important cause of perina- and furthermore, such measures could bique.17–19 Furthermore, doubts have tal morbidity and mortality in resource contribute to reduced HIV transmis- also been raised about the accuracy of the poor settings. Adverse infant or fetal sion.8, 14 currently used syphilis screening tests, outcomes arise in 50–80% of pregnan- Every year, about 1.6 million preg- such as the RPR, especially in popula- cies that survive beyond 12 weeks of 20 1–3 nant women with syphilis remain undi- tions with a high prevalence of HIV gestation, especially if pregnancy agnosed in sub-Saharan Africa, including and malaria.21 coincides with the early stages of infec- more than one million attending antena- The recent introduction of rapid 4–6 tion. Syphilis is also a substantial cause tal care.15 Syphilis — as diagnosed by a immunochromatographic strip (ICS) to of adult morbidity and might increase positive rapid plasma reagin (RPR) test screen for treponemal infection would the risk of human immunodeficiency — at the first antenatal visit in Mozam- allow syphilis to be both diagnosed and virus (HIV) transmission.7, 8 bique has a prevalence of about 10% treated in a single visit.22, 23 Antenatal Syphilis control is facilitated by the for the country as a whole and 15% for clinic nurses can do the ICS test in health availability of inexpensive and sensitive Sofala Province, where our study was facilities without a laboratory. Unlike diagnostic tests and effective and afford- conducted.16 RPR reagents, the ICS can be stored at able treatment.7, 9–12 Antenatal screening Scarcity of laboratory services, staff, room temperature and does not require and treatment for the disease is highly and training as well as late diagnosis special procedures. A price reduction to a Health Alliance International, PO Box 23, Maputo, Mozambique. Correspondence to Dr Montoya (email: [email protected]). b Departments of Medicine/Infectious Diseases, Pathobiology, Microbiology, Periodontics. University of Washington, Seattle, WA, USA. c International Health Program, Department of Health Services. University of Washington, Seattle, WA, USA. d Ministry of Health of Mozambique, Predio de governo 4o andar, Repartição de Asistencia Médica, Direcção provincial de Saúde de Sofala. Beira, Mozambique. Ref. No. 04-018663 (Submitted: 28 May 2004 – Final revised version received: 5 August 2005 – Accepted: 18 August 2005) Bulletin of the World Health Organization | February 2006, 84 (2) 97 Research Syphilis screening in Mozambique Pablo J Montoya et al. less than US$ 0.50 per test makes ICS We used a solid phase treponemal Data about HIV status were ob- a feasible option for use in settings with immunochromatographic assay that pro- tained from patients who underwent scarce resources. vides qualitative detection of antibodies voluntary counselling and testing for In this study, we aimed to: 1) com- directed towards three T. pallidum re- HIV infection as part of routine ante- pare the diagnostic accuracy 24 of ICS combinant antigens; results are obtained natal care. HIV-positive patients were and the RPR with a composite gold after 5–20 minutes. We chose the RPR as referred to specialized HIV clinics, as is standard for the detection of syphilis in our comparison test because it is widely the normal procedure in Mozambique. pregnancy (Treponema pallidum haemag- used in syphilis screening.6, 9, 25–29 Syphilis was treated with benzathine glutination assay (TPHA), RPR and Samples of genital mucocutaneous penicillin and malaria with sulfadoxine- direct immunofluorescence stain done lesions were smeared on glass slides and pyrimethamine or chloroquine, depen- at a reference laboratory); 2) compare sent to the University of Washington, dant on gestational age and in accor- diagnostic accuracy of ICS and RPR in Seattle, WA, USA to be tested with use of dance with the clinical protocols of the women with and without HIV or ma- direct immunofluorescence stain for T. Mozambique Ministry of Health.30, 31 laria; 3) compare results from the refer- pallidum (ViroStat, Portland, ME, USA). Data were analysed with Stata 7.0. ence laboratory with those from field All tests were done in accordance with We assumed that with a sample size of tests; and 4) describe operational issues manufacturers’ recommendations. Fre- 4000 women, we would obtain a preci- that affect the diagnostic accuracy of the quent supervision and assessment took sion standard error (SE) of ±3% for the tests done in health facilities. place to ensure valid and reliable results. diagnosis of active syphilis. We com- Nurses at the antenatal clinics did pared the performance of the ICSRef, Materials and methods the initial ICS (hereinafter ICSHF) dur- ICSHF and RPRHF tests with the gold We recruited participants from a popula- ing the patient’s visit. At the health fa- standard for all women, stratifying by tion of pregnant women attending their cilities, a laboratory technician who was syphilis serological group, HIV status first antenatal visit at one of six typical unaware of the results of the ICSHF did and malaria status. Differences between health facilities in Sofala Province, Mo- a first qualitative RPR test (hereinafter subgroups were calculated using c² or zambique. We chose health facilities that RPRHF). Fisher’s exact test as appropriate. We had a laboratory, that were in a region At the reference laboratory, techni- calculated crude and adjusted odds ratios with high prevalence of syphilis, HIV cians who were unaware of the results (OR) for factors associated with syphilis and malaria, and that had a high number of previous tests repeated the ICS and serological groups (i.e.,outcome) using of antenatal patients. Infrastructure at RPR tests using serum and the same logistic or multinomial logistic regres- the health facilities was basic and un- kit lots as were used at the health facil- sion analysis. like the reference laboratory, buildings ity (hereinafter ICSRef and RPRRef). The For subgroup analysis, age was at the health facilities did not have air TPHA was performed as a confirmatory treated as a categorical variable with conditioning. Mozambique Ministry of test, and a quantitative RPR was done on seven groups: <15 years, 15–19, 20–24, Health staff at the six facilities received serum that had any degree of reactivity 25–29, 30–34, 35–39, and 40 years or 3 days’ training on the study and labora- in the treponemal (ICS and TPHA) and older. Likewise, we treated number of tory procedures. non-treponemal (RPR) tests. pregnancies as a categorical variable with After providing written informed At the Beira reference laboratory, six groups: 1, 2, 3, 4, 5, and 6 or more consent, participants answered a ques- thick blood smears were stained and pregnancies. tionnaire that included questions about read quantitatively for malaria (parasite The study was approved by the their obstetric and syphilis history. They count per 500 leukocytes adjusted for Instituto Nacional de Bioética para a had an expanded physical examination, a presumed leukocyte count of 8000 Saúde in Mozambique and the Human m which included a search for mucocuta-