Impact of Age, Gender, and Pregnancy on Syphilis Screening Using the Captia Syphilis-G Assay

Retrospective comparison of false-positive result frequencies of 3 syphilis serology screening tests in pregnant and nonpregnant patients at an academic medical center in Appalachia

OBJECTIVE

This study retrospectively compared false-positive result frequencies of 3 syphilis serology screening tests and assessed whether false positivity was associated with pregnancy and age.

METHODS

Results for 3 screening tests were retrieved from the laboratory database, including rapid plasma reagin (RPR) assay between October 2016 and September 2019, BioPlex 2200 Syphilis Total immunoassay between May 2020 and January 2022, and Alinity i Syphilis TP assay between February 2022 and April 2023. The false-positive result frequencies were calculated based on testing algorithm criteria.

RESULTS

False-positive result frequency for BioPlex was 0.61% (90/14,707), significantly higher than 0.29% (50/17,447) for RPR and 0.38% (55/14,631) for Alinity (both P < .01). Patients with false-positive results were significantly older than patients with nonreactive results for RPR (median age: 36 vs 28, P < .001), but not for BioPlex or Alinity. For all 3 tests, the positive predictive values in pregnant women were lower than those in nonpregnant women or men. However, pregnant women did not exhibit a higher false-positive result frequency.

CONCLUSION

Although false-positive result frequencies were low overall for all 3 syphilis serology tests, there is a significant difference between different tests. Pregnancy was not associated with more false-positive results for all 3 tests.

CDC Laboratory Recommendations for Syphilis Testing, United States, 2024

This report provides new CDC recommendations for tests that can support a diagnosis of syphilis, including serologic testing and methods for the identification of the causative agent Treponema pallidum. These comprehensive recommendations are the first published by CDC on laboratory testing for syphilis, which has traditionally been based on serologic algorithms to detect a humoral immune response to T. pallidum. These tests can be divided into nontreponemal and treponemal tests depending on whether they detect antibodies that are broadly reactive to lipoidal antigens shared by both host and T. pallidum or antibodies specific to T. pallidum, respectively. Both types of tests must be used in conjunction to help distinguish between an untreated infection or a past infection that has been successfully treated. Newer serologic tests allow for laboratory automation but must be used in an algorithm, which also can involve older manual serologic tests. Direct detection of T. pallidum continues to evolve from microscopic examination of material from lesions for visualization of T. pallidum to molecular detection of the organism. Limited point-of-care tests for syphilis are available in the United States; increased availability of point-of-care tests that are sensitive and specific could facilitate expansion of screening programs and reduce the time from test result to treatment. These recommendations are intended for use by clinical laboratory directors, laboratory staff, clinicians, and disease control personnel who must choose among the multiple available testing methods, establish standard operating procedures for collecting and processing specimens, interpret test results for laboratory reporting, and counsel and treat patients. Future revisions to these recommendations will be based on new research or technologic advancements for syphilis clinical laboratory science.

Outcomes After Positive Syphilis Screening

BACKGROUND

Syphilis screening during pregnancy helps prevent congenital syphilis. The harms associated with false positive (FP) screens and whether screening leads to correct treatments has not been well determined.

METHODS

The population included mothers and infants from 75 056 pregnancies. Using laboratory-based criteria we classified initial positive syphilis screens as FP or true positive (TP) and calculated false discovery rates. For mothers and infants we determined treatments, clinical characteristics, and syphilis classifications.

RESULTS

There were 221 positive screens: 183 FP and 38 TP. The false discovery rate was 0.83 (95% confidence interval [CI], 0.78-0.88). False discovery rates were similar for traditional 0.83 [95% CI, 0.72-0.94] and reverse algorithms 0.83 (95% CI, 0.77-0.88), and for syphilis Immunoglobin (Ig) G 0.79 (95% CI, 0.71-0.86) and total 0.90 (95% CI, 0.82-0.97) assays. FP screens led to treatment in 2 women and 1 infant. Two high-risk women were not rescreened at delivery and were diagnosed after hospital discharge; 1 infant developed congenital syphilis. Among 15 TP women with new syphilis, the diagnosis was before the late third trimester in 14 (93%). In one-half of these women, there was concern for reinfection, treatment failure, inadequate treatment or follow-up care, or late treatment, and their infants did not achieve an optimal syphilis classification.

CONCLUSIONS

Syphilis screening identifies maternal syphilis, but limitations include FP screens, which occasionally lead to unnecessary treatment, inconsistent risk-based rescreening, and among TP mothers failure to optimize care to prevent birth of infants at higher risk for congenital syphilis.

Curry SJ, Krist AH, Owens DK, Barry MJ, Caughey AB, Davidson KW, Doubeni CA, Epling JW, Kemper AR, Kubik M, Kurth AE, Landefeld CS, Mangione CM, Phipps MG, Silverstein M, Simon MA, Tseng CW, Wong JB. Screening for Syphilis Infection in Pregnant Women: US Preventive Services Task Force Reaffirmation Recommendation Statement

IMPORTANCE

Untreated syphilis infection in pregnant women can be transmitted to the fetus (congenital syphilis) at any time during pregnancy or at birth. Congenital syphilis is associated with stillbirth, neonatal death, and significant morbidity in infants (eg, bone deformities and neurologic impairment). After a steady decline from 2008 to 2012, cases of congenital syphilis markedly increased from 2012 to 2106, from 8.4 to 15.7 cases per 100 000 live births (an increase of 87%). At the same time, national rates of syphilis increased among women of reproductive age.

OBJECTIVE

To update the US Preventive Services Task Force (USPSTF) 2009 recommendation on screening for syphilis infection in pregnant women.

EVIDENCE REVIEW

The USPSTF commissioned a reaffirmation evidence update to identify new and substantial evidence sufficient enough to change its prior recommendation. Given the established benefits and practice of screening for syphilis in pregnant women, the USPSTF targeted its evidence review on the direct benefits of screening on the prevention of congenital syphilis morbidity and mortality and the harms of screening for and treatment of syphilis infection in pregnant women.

FINDINGS

Using a reaffirmation process, the USPSTF found that accurate screening algorithms are available to identify syphilis infection. Effective treatment with antibiotics can prevent congenital syphilis and significantly decrease adverse pregnancy outcomes, with small associated harms, providing an overall substantial health benefit. Therefore, the USPSTF reaffirms its previous conclusion that there is convincing evidence that screening for syphilis infection in pregnant women provides substantial benefit.

CONCLUSIONS AND RECOMMENDATION

The USPSTF recommends early screening for syphilis infection in all pregnant women. (A recommendation).

Screening for Syphilis Infection in Pregnant Women: Updated Evidence Report and Systematic Review for the US Preventive Services Task Force

IMPORTANCE

The incidence of syphilis and congenital syphilis in the United States has increased after reaching historic lows in the early 2000s.

OBJECTIVE

To systematically review literature on the effectiveness and harms of screening for syphilis in pregnancy and the harms of penicillin treatment in pregnancy to inform the US Preventive Services Task Force.

DATA SOURCES

MEDLINE, PubMed, and the Cochrane Central Register of Controlled Trials for relevant English-language literature, published from January 1, 2008, to June 2, 2017. Ongoing surveillance was conducted through November 22, 2017.

STUDY SELECTION

Studies conducted in countries categorized as "high" or "very high" on the Human Development Index that explicitly addressed 1 of 3 a priori-defined key questions.

DATA EXTRACTION AND SYNTHESIS

Independent critical appraisal and data abstraction by 2 reviewers. Data from included studies were narratively synthesized without pooling data.

MAIN OUTCOMES AND MEASURES

Incidence of congenital syphilis; any harms of screening or penicillin treatment in pregnancy.

RESULTS

Seven studies in 8 publications were included. One observational study evaluated the implementation of syphilis screening in pregnancy in 2 441 237 women in China. From 2002 to 2012, screening for syphilis in all pregnant women increased from 89.8% to 97.2%, and the incidence of congenital syphilis decreased from 109.3 to 9.4 cases per 100 000 live births. Five studies (n = 21 795) evaluated the false-positive findings of treponemal tests and 1 study (n = 318) evaluated the false-negative findings of nontreponemal tests. These studies found that false-positives with treponemal-specific enzyme or chemiluminescent immunoassays were common (46.5%-88.2%), therefore warranting reflexive (automatic confirmatory) testing for all positive test findings. One study (n = 318) found no false-negatives with treponemal tests, and 1 study (n = 139) demonstrated the prozone phenomenon (false-negative response from high antibody titer) with rapid plasma reagin screening using undiluted samples (2.9%). No studies were identified for harms of penicillin in pregnancy.

CONCLUSIONS AND RELEVANCE

Screening for syphilis infection in pregnant women is associated with reduced incidence of congenital syphilis, and available evidence supports the need for reflexive testing for positive test results.

Syphilis in during pregnancy: association of maternal and perinatal characteristics in a region of southern Brazil

Objective:

To analyze the prevalence of syphilis in during pregnancy and its association with socioeconomic characteristics, reproductive history, prenatal and labor care, and newborn characteristics.

Method:

A retrospective, cross-sectional study based on gestational and congenital syphilis reports. A (records) linkage was performed in the Brazilian databases: “Information System for Notifiable Diseases” (Sistema de Informação de Agravos de Notificação - SINAN); “Live Births Information System” (Sistema de Informação sobre Nascidos Vivos - SINASC); and “Mortality Information System” (Sistema de Informação sobre Mortalidade - SIM).

Results:

The prevalence of gestational syphilis was 0.57%. The following associations of syphilis in pregnancy were found: non-white skin color/ethnicity (PR=4.6, CI=3.62-5.76); low educational level (PR=15.4; CI=12.60-18.86); and absence of prenatal care (PR=7.4, CI=3.68-14.9). The perinatal outcomes associated with gestational syphilis were prematurity (PR=1.6 CI=1.17-2.21) and low birth weight (PR=1.6; CI=1.14-2.28). Two deaths from congenital syphilis, one death from another cause and five stillbirths were reported.

Conclusion:

The results signify a long way until reaching the World Health Organization’s goal of eradicating congenital syphilis.

The Significance of Isolated Reactive Treponemal Enzyme Immunoassay in the Diagnosis of Early Syphilis

BACKGROUND

The Treponemal test algorithm for syphilis screening is widely used. A diagnostic challenge between identifying early syphilis versus a false positive signal occurs in cases where the treponemal enzyme immunoassay (EIA) is reactive and confirmatory T. pallidum particle agglutination assay is negative. We investigated the diagnostic outcome of isolated reactive EIA in patients attending a sexual health clinic.

METHODS

Results of syphilis serology tests carried out at Birmingham Whittall Street Clinic between August 10, 2010, and November 31, 2014, were reviewed. Cases with isolated EIA were routinely invited for repeat syphilis serology. Outcomes of patients with isolated EIA were reviewed and the proportion with confirmed positive syphilis serology on their repeat test identified. The number of isolated EIA cases needed to retest to identify 1 case of early syphilis was calculated.

RESULTS

A total of 121,724 syphilis screening tests were performed. Among the 1561 individual patients with reactive EIA sera, 316 (20% of total reactive tests) had isolated reactive EIA. Repeat syphilis serology results of 163 patients were reviewed; 106 patients remained with isolated reactive EIA, 50 had negative EIA test and 7 (4.3%) had confirmed reactive EIA. Of the 7 patients, 2 had evidence of early syphilis infection. The number of isolated EIA needed to retest to identify 1 case of early syphilis was 81.5 (95% confidence interval, 22.9-671.4).

CONCLUSIONS

Routine recall of patients with isolated EIA sera is not warranted. Risk of acquisition or presence of early syphilis should be assessed independently and irrespective of a negative syphilis screening test or isolated EIA.

Discordant Syphilis Immunoassays in Pregnancy: Perinatal Outcomes and Implications for Clinical Management

BACKGROUND

The reverse sequence algorithm is often used for prenatal syphilis screening by high-volume laboratories, beginning with a treponemal test such as the chemiluminescence immunoassay (CIA), followed by testing of CIA-positive (CIA(+)) specimens with the rapid plasma reagin test (RPR). The clinical significance of discordant serology (CIA(+)/RPR(-)) for maternal and neonatal outcomes is unknown.

METHODS

From August 2007 to August 2010, all pregnant women at Kaiser Permanente Northern California with discordant treponemal serology underwent reflexive testing with Treponema pallidum particle agglutination assay (TP-PA) and were categorized as "TP-PA confirmed" (CIA(+)/RPR(-)/TP-PA(+)) or "isolated CIA positive" (CIA(+)/RPR(-)/TP-PA(-)). Demographic variables and clinical data were abstracted from the medical record and compared by TP-PA status.

RESULTS

Of 194 pregnant women, 156 (80%) were CIA(+)/RPR(-)/TP-PA(-) and 38 (20%) were CIA(+)/RPR(-)/TP-PA(+). Among the 77 (49%) CIA(+)/RPR(-)/TP-PA(-) women who were retested, 53% became CIA(-). CIA(+)/RPR(-)/TP-PA(+) (n = 38) women were more likely to be older, have a prior history of sexually transmitted infections, and receive treatment for syphilis during pregnancy than women who were CIA(+)/RPR(-)/TP-PA(-) (all P < .005). Most pregnancies (189/194 [97.5%]) resulted in a live birth; there was no difference in birth outcomes according to TP-PA status and no stillbirths attributable to syphilis.

CONCLUSIONS

Most pregnant women with discordant serology were CIA(+)/RPR(-)/TP-PA(-); more than half who were retested became CIA(-). CIA(+)/RPR(-)/TP-PA(-) serology in pregnancy is likely to be falsely positive. Reflexive testing of discordant specimens with TP-PA is important to stratify risk given the likelihood of false-positive results in this population.

Improving global estimates of syphilis in pregnancy by diagnostic test type: A systematic review and meta-analysis

BACKGROUND

"Probable active syphilis," is defined as seroreactivity in both non-treponemal and treponemal tests. A correction factor of 65%, namely the proportion of pregnant women reactive in one syphilis test type that were likely reactive in the second, was applied to reported syphilis seropositivity data reported to WHO for global estimates of syphilis during pregnancy.

OBJECTIVES

To identify more accurate correction factors based on test type reported.

SEARCH STRATEGY

Medline search using: "Syphilis [Mesh] and Pregnancy [Mesh]," "Syphilis [Mesh] and Prenatal Diagnosis [Mesh]," and "Syphilis [Mesh] and Antenatal [Keyword].

SELECTION CRITERIA

Eligible studies must have reported results for pregnant or puerperal women for both non-treponemal and treponemal serology.

DATA COLLECTION AND ANALYSIS

We manually calculated the crude percent estimates of subjects with both reactive treponemal and reactive non-treponemal tests among subjects with reactive treponemal and among subjects with reactive non-treponemal tests. We summarized the percent estimates using random effects models.

MAIN RESULTS

Countries reporting both reactive non-treponemal and reactive treponemal testing required no correction factor. Countries reporting non-treponemal testing or treponemal testing alone required a correction factor of 52.2% and 53.6%, respectively. Countries not reporting test type required a correction factor of 68.6%.

CONCLUSIONS

Future estimates should adjust reported maternal syphilis seropositivity by test type to ensure accuracy.