Laboratory Evaluation of a Point-of-Care Downward-Flow Assay for Simultaneous Detection of Antibodies to Treponema pallidum and Human Immunodeficiency Virus

Abstract

dCombining the detection of syphilis and HIV antibodies into one point-of-care test integrates syphilis screening into already existing HIV screening programs, which may be particularly beneficial in settings such as antenatal care. Using the INSTI Multiplex downward-flow immunoassay, we tested 200 stored serum samples from high-risk patients enrolled in a longitudinal study on HIV infection and syphilis in Peruvian men who have sex with men and transgender women. This rapid assay detected HIV and Treponema pallidum serum antibodies with sensitivities of 100% (95% confidence interval [CI], 95.9% to 100%) and 87.4% (95% CI, 81.4% to 92.0%), respectively, and specificities of 95.5% (95% CI, 89.9% to 98.5%) and 97.0% (95% CI, 84.2% to 99.9%), respectively (n ‫؍‬ 200). The sensitivity for syphilis antibody detection was higher in patients with a rapid plasma reagin titer of >1:8 (97.3%) than in those with a titer of <1:4 (90%) or a nonreactive titer (66.7%). While syphilis, an infection caused by the spirochete Treponema pallidum, is a curable disease, it is estimated that there are 5.6 million new syphilis infections in adults annually (1) compared to approximately 2 million new HIV infections (2). Although new syphilis infections are more common, HIV screening has become a priority in low-and middle-income countries. Syphilis frequently presents atypically, which can make it difficult to clinically differentiate from other sexually transmitted infections; thus, effective diagnostic tests are crucial for correctly identifying and managing syphilis infections (3). Highly accurate diagnostic tests for HIV infection and syphilis exist, but they are often inaccessible to people living in areas with the highest burden of disease. Point-of-care tests provide an opportunity to reach those populations through tests that are inexpensive, easy to perform, and rapid, which enables same-day testing and treatment. Combining the detection of syphilis and HIV antibodies into one point-of-care test integrates syphilis screening into already existing HIV screening programs, which might be particularly beneficial in settings such as antenatal care (4).The INSTI Multiplex downward-flow immunoassay (bioLytical Laboratories, Inc., Canada) is for the simultaneous detection of HIV and T. pallidum antibodies. Results can be read in less than 1 min. Previous studies of the INSTI HIV-1/HIV-2 antibody test found it to be highly sensitive, specific, and easy to use (5-11). The INSTI Multiplex assay was developed recently, and no published data on its accuracy, feasibility, or acceptability exist yet.Using the INSTI Multiplex, we tested 200 stored (Ϫ80°C) serum samples from high-risk patients enrolled in a longitudinal study on HIV infection and syphilis in Peruvian men who have sex with men and transgender women (12). Genital lesions are a sign of primary syphilis, and 14 of the 200 serum samples were from patients who had primary syphilis, confirmed by T. pallidum DNA detection using PCR (12). The sera were tested for HIV and T. pallidum ant...

Laboratory evaluation of four HIV/syphilis rapid diagnostic tests

“…This makes the sensitivity and specificity calculations very comparable between the four assays. Sensitivities and specificities obtained for anti-HIV antibody detection (Table 2) are in line with results from earlier published laboratory evaluations for all four assays [3–7, 9, 11–14, 16–21]. For Treponema pallidum , however, the sensitivities obtained in our study were lower compared to earlier published data for all assays, while specificities were comparable.…”

“…SD Bioline previous laboratory evaluations: references [5, 7, 12–14, 16, 17, 20, 21, 23, 24]; SD Bioline previous field evaluations: references [8, 11, 15]; DPP previous laboratory evaluations: references [5, 17–19, 23]; Multiplo previous laboratory evaluations: references [5, 6, 17, 23]; Multiplo previous field evaluations: reference [10]; Insti previous laboratory evaluation: reference [9] NA Not available a range from lowest obtained sensitivity or specificity to highest…”

A systematic review and meta-analysis of studies evaluating the performance and operational characteristics of dual point-of-care tests for HIV and syphilis

“…One study was identified that evaluated the diagnostic accuracy of the INSTI Multiplex downward-flow immunoassay 48 (also called the INSTI Multiplex HIV-1/HIV-2/Syphilis Antibody Test) (bioLytical Laboratories, Canada). Using 200 archived serum specimens from high-risk individuals in Peru, the results of this study suggested a high sensitivity (100%, 95% CI 95.9% to 100%) and specificity (95.5%, 95% CI 89.9% to 98.5%) for HIV diagnosis and a slightly lower sensitivity (87.4%, 95% CI 81.4% to 92.0%) but a higher specificity (97%, 95% CI 84.2% to 99.9%) for syphilis diagnosis.…”

Reducing Uncertainty for Acute Febrile Illness in Resource-Limited Settings: The Current Diagnostic Landscape

“…Multiplex point-of-care immunoassays for HIV and syphilis as well as mosquito-borne diseases have been tested, and are commercially available for HIV and syphilis. [66][67][68][69] Using bacteriophage display libraries, epitopes for thousands of viral strains have been generated to detect exposure to almost every virus. 58 Diagnosis of neglected tropical diseases such as human African trypanosomiasis and visceral leishmaniasis has traditionally required complex or unreliable serologic methods, but lateral flow tests to replace them have now been developed and commercialized.…”