Field performance of a rapid point-of-care diagnostic test for antenatal syphilis screening in the Amazon region, Brazil

Abstract

We evaluated an immunochromatographic point-of-care (POC) syphilis test in 712 pregnant women under field conditions in remote communities of the Amazon region (Brazil), and identified risk factors for syphilis. Women were screened by POC test using whole blood obtained by fingerprick, the fluorescent treponemal antibody absorption (FTA-Abs) test as the gold standard and the Venereal Diseases Research Laboratory (VDRL) test to determine test performance in active syphilis. Multivariate analysis was conducted to identify factors associated with syphilis infection. Among women, 2.2% had syphilis (positive FTA-Abs) and 0.8% active syphilis (FTA-Abs and VDRL positive). In all, 2.2% of samples were positive by the POC test. The sensitivity, specificity, positive and negative predictive values were 62.5% (95% confidence interval [CI]: 38.6-81.5), 99.1% (95% CI: 98.1-99.6), 62.5% (95% CI: 38.6-81.5) and 99.1% (95% CI: 98.1-99.6), respectively. The POC test identified 62.5% (10/16) of syphilis cases, 66.7% (4/6) of active syphilis cases and all high-titre syphilis cases (VDRL > 1:8). Older age was associated with syphilis infection. The rapid test performed moderately well as a screening tool for low-risk populations. This combined with on-site testing and same day treatment could expand antenatal syphilis screening programmes in distant communities characterized by difficult access to antenatal services and infrequent clinical follow-up visits.

The role of Point-of-Care testing in the diagnosis of syphilis

“…Lately, it seems that this may be overcome with the availability of treponemal and non-treponemal POC tests that may be used successfully in areas with unfavourable conditions for a normal diagnostic laboratory. Overall, these tests have shown to have good sensitivities and specificities [30,32,33,47] and to increase screening in different population groups from pregnant women to sex workers, MSM and drug addicts, and other outreach populations anywhere in the world [22,25,44,[54][55][56]. The tests are generally well received by local health care workers and clients in places where studies have been performed [24,25,40,49,56].…”

“…In those studies, sensitivities of the POCTT varied from around 63 % in the first studies to almost 100 % [30][31][32][33]36,39,44,45], with specificities varying from around 90 % to 100 % in the most recent studies. The tests' increasing performance over the years is associated not only with the development of better tests but also with better quality control, one of the most important steps, especially when taking into consideration that these tests are to be used mainly in remote regions.…”

“…The same was found by MacPherson et al [54] in injecting-drug users (IDUs), MSM, and UK Africans, who successfully reached these target groups, many of whom would not have been tested otherwise. Studies performed in Bangalore, India, and the Amazon region of Brazil [22,44,55,56] showed that POCT was helpful in alleviating the impact of syphilis in both pregnant and non-pregnant outreach populations, including high-risk individuals such as sex workers. Although this was also true in Guatemala [42], there screening uptake was limited by a shortage of health care workers and poor supply chain management.…”

Desempeño de una prueba rápida para el diagnóstico de sífilis en mujeres puérperas

“…La prueba rápida realizada siguiendo los protocolos del fabricante es una herramienta de detección para las poblaciones de bajo riesgo. Esto, combinado con pruebas en el lugar y en el mismo día de tratamiento podría ampliar los programas de detección de sífilis prenatal y en puérperas en comunidades distantes que se caracterizan por la dificultad de acceso a los servicios de atención prenatal y visitas de seguimiento clínico poco frecuentes y en sistemas de salud que cuentan con pocos recursos (4,26,27). Aunque las pruebas y el tratamiento de la sífilis en el embarazo deben estar universalmente disponibles, un estudio de la OMS revela que más de la mitad de los embarazos en mujeres con sífilis dará lugar a un resultado adverso.…”

A better definition of active syphilis infection

“…However, this definition of active syphilis infection should be reconsidered. Many studies have shown [11,[13][14][15][16][17] that active syphilis infection should be defined by positive treponemal tests and any positive RPR/VDRL titer, rather than only by a VDRL Clinica Chimica Acta 444 (2015) 1-2 titer of ≥ 1:8. For example, Larsen et al [1] believed that a reactive or weakly reactive VDRL result usually indicates an active infection.…”