Diagnostic performance of two rapid tests for syphilis screening in people living with HIV in Cali, Colombia

Correction: Diagnostic performance of two rapid tests for syphilis screening in people living with HIV in Cali, Colombia

[This corrects the article DOI: 10.1371/journal.pone.0282492.].

Accuracy of capillary blood sampling for diagnosing syphilis infection

Capillary blood collection presents advantages such as reduced invasiveness over venous serum for syphilis diagnosing. This study aimed to compare diagnostic accuracy between capillary and venous blood samples for syphilis diagnosis. Individuals aged ≥ 18 years were included in a cross-sectional study. Syphilis screening was done using Rapid tests (RT) followed by collection of serum capillary and venous samples for VDRL and TPHA test. Sensitivity, specificity, and Kappa coefficient were calculated. Of 191 participants, 115 RT + and 76 RT-. Diagnostic properties did not significantly differ between capillary and venous samples. Capillary VDRL showed 99% sensitivity and 100% specificity, mirroring TPHA results. Furthermore, there was significant agreement between sample types for both serological tests (p < 0.001). Capillary sampling offers comparable diagnostic accuracy to venous collection, regardless of serum quality. Capillary sampling holds promise, particularly in developing countries and large-scale testing initiatives.

Laboratory evaluation of oral fluid for syphilis screening among clinic users from Lima, Peru

Serological tests for syphilis require equipment unavailable in many health centers; however, point-of-care testing facilitates rapid screening using finger-prick whole blood samples. A further improvement could be oral fluid for ease of use. We evaluated the performance of treponemal antibody point-of-care testing for syphilis screening using oral fluid samples. We recruited users of STI clinics in Lima, Peru. We collected oral fluid using the OraSure collection device (OraSure Technologies Inc., USA) according to the manufacturer's instructions and serum from each participant. Oral fluid and serum were analyzed using the SD Bioline Syphilis 3.0 rapid test (Standard Diagnostics Inc., Korea). Serum was also tested using RPR (RPR slide test, Wiener Laboratorios SAIC, Argentina) and TPPA (Serodia, Fujirebio Diagnostics Inc., Japan). We assessed oral fluid rapid test overall percent agreement, sensitivity, specificity, and Kappa coefficient against serum SD Bioline Syphilis, TPPA, and RPR. Among 323 participants, nearly half (51.3%) reported prior syphilis. The overall percent agreement, sensitivity, specificity, and Kappa coefficient of oral fluid were 71.0% (95% CI: 65.6%-75.8%), 78.1% (71.1%-83.7%), 63.5% (55.8%-70.6%), and 0.42% (0.32%-0.52%), respectively, versus serum SD Bioline Syphilis. A similar performance was obtained versus serum TPPA. When limiting the sample to TPPA-reactive with RPR titer ≥1:8, the sensitivity increased to 88.1% (75.0%-94.8%), whereas the specificity did not vary (65.3% [57.2%-72.6%]). We observed a good performance of the rapid treponemal test using oral fluid. Further investigations are needed to improve the specificity of oral fluid as a potential sample for accurate syphilis screening.IMPORTANCEPoint-of-care tests are essential for rapid and efficient screening of syphilis, especially in low-resource settings. Oral fluid specimens offer a noninvasive, accessible, and practical alternative to traditional blood samples. Our study evaluated the performance of a rapid treponemal test using oral fluid specimens. We found that the rapid treponemal test using oral fluid had good sensitivity compared with the rapid treponemal test using serum and the non-treponemal RPR test. This suggests that oral fluid could be a viable option for syphilis screening, facilitating broader and faster access to diagnosis and treatment. However, further studies are needed to improve the specificity of this method to ensure accurate screening in diverse clinical scenarios.

Treponema pallidum genetic diversity and its implications for targeted vaccine development: A cross-sectional study of early syphilis cases in Southwestern Colombia

BACKGROUND

Venereal syphilis, caused by the spirochete Treponema pallidum subsp. pallidum (TPA), is surging worldwide, underscoring the need for a vaccine with global efficacy. Vaccine development requires an understanding of syphilis epidemiology and clinical presentation as well as genomic characterization of TPA strains circulating within at-risk populations. The aim of this study was to describe the clinical, demographic, and molecular features of early syphilis cases in Cali, Colombia.

METHODS AND FINDINGS

We conducted a cross-sectional study to identify individuals with early syphilis (ES) in Cali, Colombia through a city-wide network of public health centers, private sector HIV clinics and laboratory databases from public health institutions. Whole blood (WB), skin biopsies (SB), and genital and oral lesion swabs were obtained for measurement of treponemal burdens by polA quantitative polymerase chain reaction (qPCR) and for whole-genome sequencing (WGS). Among 1,966 individuals screened, 128 participants met enrollment criteria: 112 (87%) with secondary (SS), 15 (12%) with primary (PS) and one with early latent syphilis; 66/128 (52%) self-reported as heterosexual, while 48 (38%) were men who have sex with men (MSM). Genital ulcer swabs had the highest polA copy numbers (67 copies/μl) by qPCR with a positivity rate (PR) of 73%, while SS lesions had 42 polA copies/μl with PR of 62%. WB polA positivity was more frequent in SS than PS (42% vs 7%, respectively; p = 0.009). Isolation of TPA from WB by rabbit infectivity testing (RIT) was achieved in 5 (56%) of 9 ES WB samples tested. WGS from 33 Cali patient samples, along with 10 other genomic sequences from South America (9 from Peru, 1 from Argentina) used as comparators, confirmed that SS14 was the predominant clade, and that half of all samples had mutations associated with macrolide (i.e., azithromycin) resistance. Variability in the outer membrane protein (OMP) and vaccine candidate BamA (TP0326) was mapped onto the protein's predicted structure from AlphaFold. Despite the presence of mutations in several extracellular loops (ECLs), ECL4, an immunodominant loop and proven opsonic target, was highly conserved in this group of Colombian and South American TPA isolates.

CONCLUSIONS

This study offers new insights into the sociodemographic and clinical features of venereal syphilis in a highly endemic area of Colombia and illustrates how genomic sequencing of regionally prevalent TPA strains can inform vaccine development.

Prevalence of HIV, Treponema pallidum and Their Coinfection in Men Who Have Sex with Men, Medellín-Colombia

Introduction

In Colombia, HIV and gestational syphilis are notifiable events; however, they are poorly investigated infections in men who have sex with men (MSM).

Objective

To determine the prevalence of HIV, Treponema pallidum, and their co-infection in MSM treated at a Health Services Provider Institution (HSPI) specialized in infectious diseases from Medellín.

Methods

Cross-sectional study with 3454 MSM. Prevalence was determined with its 95% confidence interval; associated factors were identified using Fisher's Exact test, Pearson's Chi-square, and trend Chi-square. Multivariate adjustment was performed using logistic regression. Analyses were performed using SPSS 29.0.

Results

The prevalence of HIV was 5.7%, T. pallidum 0.7%, and co-infection 0.6%. The prevalence of HIV was higher in MSM aged between 24-40 years (7.5%), with technical or university studies (10.0%), without health insurance affiliation (12.4%), and those who have had a sexual partner with HIV (36.2%). T. pallidum was higher in MSM without health insurance affiliation (3.4%), who had sexual relations with people diagnosed with an STI (5.9%), and a sexual partner with HIV (12.1%). Co-infection was higher in MSM without health insurance affiliation (2.7%), and those who had a partner with HIV (11.2%).

Conclusion

Compared with the general Colombian population, MSM have a higher risk of HIV, but are similar to T. pallidum. The identification of the main associated factors in each infection demonstrates the need to prioritize subgroups of MSM that show greater vulnerability to these events. This research demonstrates the urgency of implementing health education strategies in MSM who have a sexual partner with HIV or other STIs. Large gaps were also evident in the magnitude of the three events according to the health insurance affiliation regime, which demonstrates problems of social and health injustice, especially with MSM without health insurance affiliation.