Serologic Response to Treatment in Human Immunodeficiency Virus-Negative Syphilis Patients Using Automated Serological Tests: Proposals for New Guidelines

A Longitudinal Case Study of Concurrent Infection with Syphilis and Human Immunodeficiency Virus During the Early Phase

Due to the low incidence of concurrent human immunodeficiency virus (HIV) and syphilis infection identified during the early phase, such as window period (WP), little is known about the clinical manifestations, diagnosis, and treatment efficacy at very early stages. One longitudinal study was conducted in a 42-year-old blood donor who was concurrently infected with syphilis and HIV. This blood donor was treated with a penicillin-based regimen and early antiretroviral therapy (ART). Sequential serological and nucleic acid tests were performed and the results were comparatively analyzed. A regular male donor who had two occasions of high-risk sexual behaviors 41 and 35 days before donation donated whole blood at the Shenzhen Blood Center. ART was initiated at the 28th day after donation (DAD), and syphilis treatment was received at the 49th DAD. Microbiological analysis using a fourth-generation anti-HIV enzyme-linked immunosorbent assay (ELISA) (4th GAHE) and electro-chemiluminesent immunoassay indicated a positive signal at the 6th DAD, while a third-generation anti-HIV ELISA (3rd GAHE) showed positive at the 26th DAD. All nucleic acid testing (NAT) for HIV RNA were reactive except the minipool NAT of 6 pooled samples at 117th DAD. The HIV viral load declined more than 4-log in copies per milliliter over 3 months, until reaching nondetectable levels at 246th DAD. Nevertheless, HIV-1 DNA was still detectable at 403rd DAD. Among all methods utilized, anti-treponema pallidum ELISA detected syphilis infection at the earliest time. A successful serological response to syphilis treatment was reached around the 80th DAD. Concurrent infection with syphilis and HIV during early phases did not significantly change the sensitivity of reagents in detection nor alter the therapeutic efficacy for the treatment of both pathogens, but might result in delayed HIV serological WP.

Clinical efficacy and tolerability of 1.5 g/day oral amoxicillin therapy without probenecid for the treatment of syphilis

OBJECTIVES

Intramuscular benzathine penicillin G is not available in certain countries. In a previous report, 3 g/day amoxicillin with probenecid was shown to be effective in treating syphilis in patients with HIV; however, 7.3% of patients changed their therapy owing to adverse events. The objective of this study was to assess the clinical efficacy and tolerability of 1.5 g/day amoxicillin without probenecid for the treatment of syphilis.

METHODS

The routine clinical records of patients diagnosed with syphilis and treated with 1.5 g/day amoxicillin at a tertiary care hospital between 2006 and 2018 were retrospectively analysed. Syphilis was diagnosed if serum rapid plasma reagin (RPR) titres were ≥8 RU and the Treponema pallidum latex-agglutination test was positive. Serological cure was defined as a ≥fourfold decrease in the RPR titre within 12 months in symptomatic early syphilis and within 24 months in latent syphilis.

RESULTS

Overall, 138 patients (112 with HIV) were analysed. The percentages of primary, secondary, early latent, late latent and latent syphilis of unknown duration were 8.0%, 50.0%, 25.4%, 5.8% and 10.9%, respectively. The median treatment duration was 4.5 weeks (IQR 4-8 weeks), which was not related to the stage of syphilis. Two patients (1.5%) changed treatment due to skin rash. The rate of serological cure was 94.9% (131/138; 95% CI 89.8% to 97.9%) overall; 93.8% (105/112; 95% CI 87.5% to 97.5%) in patients with HIV and 100% (26/26; 95% CI 86.8% to 100%) in patients without HIV. Treatment duration was not related to the treatment efficacy.

CONCLUSION

The regimen of 1.5 g/day amoxicillin without probenecid is highly effective with a low switch rate in patients with and without HIV.

Utility of rapid plasmin reagin titres in assessing treatment response and re-infection for infectious syphilis

Background The rapid plasma reagin (RPR) assay is commonly used as a surrogate marker of infectious syphilis, but is non-specific, slow to change and variable in its rate of decline post treatment.

METHODS

Within an urban sexual health service testing predominantly men who have sex with men, a file review of RPR changes was undertaken in all subjects who had a dilution level of ≥1:4, between January 2015 to the end of December 2018.

RESULTS

Overall, 248 cases of infectious syphilis were identified in 215 subjects (165 HIV seropositive, 50 HIV seronegative). Among unique-subject cases with follow-up RPR recorded, seroreversion to a non-reactive titre was achieved in only 42.3% (71/168) cases at a median of 235 days (interquartile range: 138-348 days) and was significantly less likely if patients had HIV infection (P = 0.02), late latent syphilis (P = 0.003) or a subsequent syphilis infection (P < 0.0001). Having HIV infection (P = 0.03) or a subsequent episode of syphilis (P = 0.01) were associated with a lower likelihood of documented cure.

CONCLUSIONS

The slow decay in RPR titres post therapy and the inability of a significant number of subjects to achieve a non-reactive result over time makes RPR a poor test for assessing the adequacy of treatment or in diagnosing re-infection, especially in populations having repeated and frequent risk exposures. As the number of syphilis cases continue to climb, better tests that accurately assess pathogen presence are urgently needed.

Usefulness of Automated Latex Turbidimetric Rapid Plasma Reagin Test for Diagnosis and Evaluation of Treatment Response in Syphilis in Comparison with Manual Card Test: a Prospective Cohort Study

The usefulness of an automated latex turbidimetric rapid plasma reagin (RPR) assay, compared to the conventional manual card test (serial 2-fold dilution method), for the diagnosis of syphilis and evaluation of treatment response remains unknown. We conducted (i) a cross-sectional study and (ii) a prospective cohort study to elucidate the correlation between automated and manual tests and whether a 4-fold decrement is a feasible criterion for successful treatment with the automated test, respectively, in HIV-infected patients, from October 2015 to November 2017. Study i included 518 patients. The results showed strong correlation between the two tests (r = 0.931; P < 0.001). With a manual test titer of ≥1:8 plus a positive Treponema pallidum particle agglutination (TPPA) test as the reference standard for diagnosis, the optimal cutoff value for the automated test was 6.0 RPR units (area under the curve [AUC], 0.998), with positive predictive value (PPV) of 92.5% and negative predictive value (NPV) of 99.4%. Study ii enrolled 66 men with syphilis. Their RPR values were followed up until after 12 months of treatment. At 12 months, 77.3% and 78.8% of the patients achieved a 4-fold decrement in RPR titer by the automated and manual test, respectively. The optimal decrement rate in RPR titer by the automated test for a 4-fold decrement by manual card test was 76.54% (AUC, 0.96) (PPV, 96.1%; NPV, 80.0%). The automated RPR test is a good alternative to the manual test for the diagnosis of syphilis and evaluation of treatment response and is more rapid and can handle more specimens than the manual test without interpersonal variation in interpretation.