ORIGINAL ARTICLEPerformance of the rapid plasma reagin and the rapidsyphilis screening tests in the diagnosis of syphilis in fieldconditions in rural AfricaB West, G Walraven, L Morison, J Brouwers, R Bailey.............................................................................................................................Sex Transm Infect2002;78:282–285Objectives: To assess the rapid plasma reagin (RPR) test performance in the field and to evaluate anew rapid syphilis test (RST) as a primary screen for syphilis.Methods: 1325 women of reproductive age from rural communities in the Gambia were tested forsyphilis seropositivity using a RPR 18 mm circle card and a RST strip. Within 1 week a repeat RPR anda TPHA test were carried out using standard techniques in the laboratory.Results: Comparing field tests to a diagnosis of “active” syphilis defined as laboratory RPR and TPHApositive, the RPR test was 77.5% sensitive and 94.1% specific; the RST was 75.0% sensitive and 95.2%specific. The RST was easier to use and interpret than the RPR test especially where field conditionswere difficult. In this setting with a low prevalence of syphilis in the community (3%), the chance ofsomeone with a positive test being confirmed as having serologically active syphilis was less than 50%for both tests.Conclusions: The appropriateness of syphilis screening using RPR testing in antenatal clinics andhealth centres should be questioned if there is a low prevalence in the population, conditions for test-ing are poor, and resources limited. There is still an urgent need for an appropriate rapid syphilis testfor field use.The rapid plasma reagin (RPR) 18 mm circle card test forsyphilis is used as a screening test in many antenatal clinicand health facilities in the developing world. Although itis easy to perform and inexpensive it may be difficult to inter-pret and requires training of health personnel to ensure test-ing is car ried out and results are read correctly. The testspecificity can be limited owing to the non-specific nature ofthe cardiolipin antigen as biological false positives occur; thesecan be due to viral infections, malaria, and pregnancy.1Addi-tionally, false negatives may occur both in early primarycases1and in patients with secondary syphilis, as a result ofprozone reactions2; this may limit the sensitivity of the test. Inmany developing country settings where the RPR test wouldbe useful as a screening test, such as antenatal clinics, qualitycontrol procedures are suboptimal or lacking entirely and therate of false positives and false negatives associated with theuse of the test (and consequent overtreatment or undertreat-ment for syphilis) may be higher under operational conditionsthan that anticipated from research reports. We assessed theRPR test performed under field conditions against RPR/TPHAtesting performed in a well appointed laboratory. Testing wascar ried out in the Gambia, where the national prevalence ofserologically active syphilis was recorded as 2.8% in a survey in1995 (O’Donovan et al, unpublished data) but has beenreported as high as 7% in 15–34 year old women in somedistricts.3We also evaluated the performance of a rapid syphi-lis test (RST, Quorum Diagnostics, Vancouver, BC, Canada) asa primary screen. The RST is a one step immunochromato-graphic strip test, utilising a 47 kDa recombinant antigen ofTreponema pallidum to detect antibody, developed by OmegaDiagnostics in association with the Programme for Appropri-ate Technology in Health (PATH) and UNAIDS, SexuallyTransmitted Diseases Diagnostics Initiative.MATERIALS AND METHODSA total of 1325 women aged 15–54 participated in a largecommunity based reproductive heath survey in 20 villages inthe Farafenni area of the Gambia, which is describedelsewhere.4Syphilis testing was included as part of the survey.For this testing a field laboratory was set up in each village. Allnecessary equipment and consumables were transported dailyto the site being surveyed. A portable generator provided elec-tricity for the centrifuge and shaker. All reagents, RPR kits,rapid syphilis test strips, and samples collected were kept in acool box that was replenished with ice packs daily.For RPR testing a 10 ml venous blood sample was collectedinto a plain vacutainer, allowed to clot for about 15 minutes,and centrifuged for 10 minutes at 2000 g. A standard RPR 18mm circle card test (Quorum Diagnostics) was carried out,mixing one drop of serum with one drop of RPR reagent, mix-ing on a shaker for 8 minutes, and read in the best availablelight. Positive and negative control sera were included in eachday’s testing.For RST testing, 100 μl of serum was aliquoted into a freshserum tube. A RST strip was removed from the foil pouch andadded to the tube. This was left for 15 minutes and the resultsread, according to the manufacturer’s guidelines. Where thesera reacts with the Treponema pallidum recombinant antigensin the strip a double pink line results and these were read aspositive. Sera were regarded as negative if only the single con-trol line was visible. If no pink line occurred the test was dis-carded as invalid.At the end of each day samples were returned to the wellequipped laboratory at the MRC Laboratories field station atFarafenni, which has a constant power and water supply.Samples were received, catalogued, and stored frozen. Within1 week RPR and TPHA testing was carried out using standardtechniques. The same laboratory assistant performed the testsin the laboratory as in the field but did not have access to fieldresults.The TPHA was a standard Fujeriebo test (Mast Laboratories,UK). Sera were diluted to 1/160 and mixed with sensitised andunsensitised red blood cells. This was read after 1 hour at roomtemperature. Sera were considered positive if agglutinationSee end of article forauthors’ affiliations.......................Correspondence to:Dr B West, MRCLaboratories, PO Box 273,Banjul, Gambia;[email protected] for publication1 March 2002.......................282www.sextransinf.com on 30 March 2005 sti.bmjjournals.comDownloaded fromoccur red with sensitised cells only. Samples were consideredvoid if agglutination occurred with unsensitised cells.RESULTSFrom the 1325 serum samples obtained, 1295 samples wereRPR tested in the field, and all 1325 samples were tested in thelaboratory; the 30 women not screened in the field were revis-ited and offered treatment if positive results were subse-quently