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Rapid Plasma Reagin Titer Variation in the 2 Weeks After Syphilis Therapy

Holman, Katherine M. MD*,†; Wolff, Mark PhD; Seña, Arlene C. MD, MPH§; Martin, David H. MD; Behets, Frieda PhD, MPH§,‖; Van Damme, Kathleen MD; Leone, Peter MD§; McNeil, Linda MA**; Gehrig, Meredyth L. BS; Hook, Edward W. III MD

doi: 10.1097/OLQ.0b013e3182536574
Original Study

Background: Serologic tests for syphilis results at the time of diagnosis are the basis for evaluating response to syphilis therapy. After treatment, however, serologic tests for syphilis titers may continue to increase for several weeks. We evaluated rapid plasma reagin (RPR) titer variation during the 14 days after therapy using data from a recent large, prospective randomized controlled trial.

Methods: Prospectively enrolled participants in North America and Madagascar with primary, secondary, or early latent syphilis were randomly assigned to penicillin, doxycycline (in the case of penicillin allergy), or azithromycin treatment. Blood for RPR analysis was drawn at days 0, 7, and 14 posttreatment. All RPR titers were determined simultaneously at a central laboratory.

Results: Four hundred and seventy patients had data available for at least 2 of 3 RPR measurements. Overall, 20% of patients showed a titer increase of at least 1 dilution in the 14 days after therapy. The greatest proportion of titer increases following therapy was observed in patients with primary syphilis. Comparing outcome of therapy using the initial (day 0) RPR titer versus the maximal RPR titer (during 14 days) resulted in outcome reclassification in 2.98% of participants.

Conclusions: Despite the fact that about 20% of early syphilis patients had increases in RPR titers immediately after treatment, these changes rarely influenced assessment of therapeutic outcome. Only 3% of patients treated would have been reclassified.

From the *Department of Quality Management, Birmingham VA Medical Center, Birmingham, AL; Division of Infectious Diseases, Department of Medicine, University of Alabama at Birmingham, Birmingham, AL; Emmes Corporation, Rockville, MD; §Division of Infectious Diseases, Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC; Division of Infectious Diseases, Department of Medicine, Louisiana State University, Baton Rouge, LA; Departments of Medicine and Epidemiology, University of North Carolina at Madagascar, Antananarivo, Madagascar; and **Family Health International, Research Triangle Park, NC

The authors acknowledge the following: Carolyn Deal, PhD, Nancy Padian, PhD, and Peter Wolff, MHA, Sexually Transmitted Infections Clinical Trials Group Executive Committee; Willard Cates, MD, MPH, Myron Cohen, MD, and Walter E. Stamm, MD, Sexually Transmitted Diseases Clinical Trials Unit Executive Committee; Emil Gotschlich, MD, Kenyon Burke, EdD, Helen Lee, PhD, Larry Moulton, PhD, and Peter Rice, MD, Data Safety and Monitoring Board; Lihan Yan, Melinda Tibbals, Robin Cessna, Carol Smith, and Jamie Winestone, EMMES Corporation; Nincoshka Acevedo, BS, Florence Carayon, MA, and Jill Stanton, BA, Family Health International; Carol Langley, MD, Janet N. Arno, MD, IN University School of Medicine; Tomay Mroczkowski, MD, Stephanie Taylor, MD, Barbara Smith, RN, LA State University; Carolyn Deal, PhD, Penny Hitchcock, DVM, Barbara Saverese, RN, Peter Wolff, MHA, National Institutes of Allergy and Infectious Disease; Joan Stephens, RN, Anna Lee Hughes, RN, Tracey Burkett, CRNP, Connie Lenderman, MT (ASCP), MBA, Paula B. Dixon, Grace Daniels, and Sharron Hagy, University of Alabama at Birmingham/Jefferson County Department of Health; Heidi Swygard, MD, Karen Lau, FNP, Christopher Bernart, PA, University of North Carolina at Chapel Hill; Bodo Sahondra Randrianasolo, MD, Mbolatiana Soanirina, MD, Michèle Raharinivo, Felasoa Noroseheno Ramiandrisoa, MD, Ny Lovaniaina Rabenja, MD, Herinjaka Andrianasolo, Roméo Rakotomanga, Tahiana Rasolomahefa, Norbert Ratsimbazafy, MD, Zo Fanantenana Raharimanana, MD, Verolanto Ramaniraka, MD, Marina Rakotonirina, Tiana Ravelohanitra, Andrianiseta Rakotomihanta, Jacqueline Hortensia Rajaonarison, Lucienne Rasoamanana, Elyse Rasoanijanahary, Charlotte Razanasolonambinina, Olivier Claret Raoelina, MD, Naina Ranaivo, MD, Angele Zanatsoa, Claire Fety, Cynthai Mamy, Bruno Raoelina, Esther Solovavy, Justine, Julienne Rasoamarovavy, Diana Ratsiambakaina, MD, Agnè Ramaroson, MD, Theodosie Tombo, David Noelimanana, Florence Raeliarisoa, Gilbert Razaka Sadiry, Bacar Soumaely, Bernard, Justin Ranjalahy Rasolofomanana, Lala Rakotondramasy, Falimanantsoa Sylvain Ramandiarivony, Hobitiana Rakotoarimanan, Lucie Razanamiandrisoa, University of North Carolina-Madagascar; Jocelyne Andriamiadana, MD, USAID Madagascar; and Institut Pasteur de Madagascar, The Ministry of Health, Madagascar.

Supported by the National Institute of Allergy and Infectious Diseases at the National Institutes of Health (grant number N01 A1 75329, Myron Cohen, MD, PI) and the STI Clinical Trials Group (grant number HHSN 26620040073C, Edward W. Hook, III, MD, PI).

Potential Conflicts of Interest: K.H., M.W., A.S., F.B., K.V.D, L.M., and M.G. declare no conflict of interest. D.M. is a share holder in Merck and has been a consultant to Cempra Pharma. P.L. has received research funding from GSK, Abbott Diagnostics, Norvartis and Trinity Diagnostics and has been on the speakers' bureaus for GSK, Norvartis and Abbott Diagnostics. E.W. has received research funding from GenProbe, Becton-Dickinson, Roche Molecular Diagnostics, Siemens Diagnostics, and has been on the speakers' bureaus for GSK, Norvartis and Abbott Diagnostics.

Correspondence: Katherine M. Holman, MD, Division of Infectious Diseases, University of Alabama at Birmingham, 1900 University Blvd THT 229, Birmingham, AL 35294. E-mail:; or Edward Hook, III, MD, Division of Infectious Diseases, University of Alabama at Birmingham, 1900 University Blvd THT 229, Birmingham, AL 35294. E-mail:

Received for publication January 9, 2012, and accepted February 29, 2012.

Syphilis is a relatively common, chronic infectious disease of public health importance. In addition to direct morbidity associated with infection, syphilis may be transmitted to sexual partners and to unborn children of infected mothers. Syphilis also is associated with increased risk for HIV transmission.1 US syphilis rates have risen steadily through the past decade.2

Serological testing for antibodies against Treponema pallidum is the most widely used means for syphilis diagnosis. Repeated determination of nontreponemal (i.e., rapid plasma reagin [RPR], Venereal Disease Research Laboratory test) serologic test for syphilis (STS) titers is recommended to evaluate response, with a 4-fold (2 dilution) decrease from baseline and/or seroreversion in 12 months after treatment representing an appropriate response to therapy/serologic cure.3 In most settings, the nontreponemal STS titer present at treatment is used to evaluate subsequent therapeutic response. However, it is possible that antitreponemal antibody concentrations may continue to increase for a period after effective therapy.4 To evaluate the frequency with which STS titers increased after early syphilis therapy, we analyzed weekly serologic test results obtained on 3 occasions from >400 patients in a recent therapeutic trial that compared benzathine penicillin G with azithromycin for early syphilis therapy.

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Data collected as part of an open-label, randomized controlled trial conducted from June 2000 to March 2009 at 5 sexually transmitted disease clinics in North America and 3 clinics in Madagascar were analyzed. Methods, including details regarding recruitment, therapeutic intervention, and clinical assessment, were previously described.5The protocol was approved by the Institutional Review Board at the University of Alabama at Birmingham and at each participating site.

Briefly, participants with primary, secondary, or early latent syphilis were randomized to treatment with single doses of benzathine penicillin, 2.4 million units intramuscularly, or azithromycin (2.0 g orally). Participants with reported penicillin allergy were randomized to doxycycline, 100 mg orally twice daily for 14 days, or azithromycin, 2.0 g orally. Follow-up visits for RPR testing were scheduled at days 7 and 14, and 3 and 6 months after treatment. Sera to determine study-defined treatment outcomes were stored frozen, and all RPR testing was performed same day at the University of Alabama at Birmingham central laboratory according to accepted methods.6

The primary outcome of the trial was serological response to therapy at 6 months. To evaluate response to treatment, the maximal RPR titer during 3 visits occurring in the 14 days after therapy (i.e., day of treatment, 7 days and 14 days) was used as the baseline for analysis. Serological cure was defined as either negative RPR or ≥4-fold (2 dilutions) decrease in titer (no participants had recurrent signs of infection); treatment failure was defined as ≥4-fold increase in RPR titer without clear history of reexposure. Serological nonresponse or serofast status was defined as no more than a 2-fold (1 dilution) increase or decrease from baseline. As specified in the protocol, those participants defined as treatment failure or serological nonresponse were retreated at 6 months with benzathine penicillin or doxycycline, if penicillin allergic.

The study population for this report is participants with serological data at the 6 months visit after treatment and without a change in eligibility status before the 6-month visit. Statistical analysis was performed using SAS Software Version 9.2 (SAS Institute, Inc., Cary, NC).7 P values are based on χ2 tests obtained from relevant contingency tables. We determined the proportions of participants with an increase in RPR titer during the 14 days after syphilis therapy.

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A total of 470/517 (90.9%) patients had data for at least 2 of 3 RPR measurements during their first 2 weeks of study participation and completed the 6-month follow-up without a change in protocol status. Selected demographic characteristics are presented in Table 1. Median RPRs at diagnosis, stratified by stage, were primary 1:16, secondary 1:64, and early latent 1:32 (Fig. 1). Overall, 20.2% (95) of patients showed a titer increase in the 14 days after therapy (Table 2). Of these, 88.2% (84) demonstrated an increase of 1 dilution, whereas in 11.8% (11) RPR titers increased ≥2 dilutions. Individuals with the earliest stages of syphilis were more likely to experience RPR increases in the 2 weeks after therapy, with 30.5% of participants treated for primary syphilis experiencing an increase in RPR titers, whereas the proportion of secondary and early latent syphilis patients was about 17% and 16%, respectively (P = 0.005).

Table 1

Table 1

Figure 1

Figure 1

Table 2

Table 2

We compared the outcome of therapy (i.e., cure, serofast, failure) at 6 months using both a “clinical definition,” the initial titer at the time of treatment, and a “research definition,” the maximal titer obtained during the 14 days after treatment. When the 2 definitions were compared, the outcome changed in only 14 participants (2.98%). Thirteen changed from serofast (clinical) to cure (research) and one changed from failure (clinical) to serofast (research) (Table 3). Increased RPR titers in the 2 weeks after therapy did not occur in all patients with treatment failure. Of the 5 participants classified as serological treatment failures,5 only one had a single dilution rise in RPR titer in the 14 days after therapy. However, at the time of defined treatment failure, this patient's RPR titer had increased by 3 dilutions from the initial titer.

Table 3

Table 3

Selected characteristics of participants with a rise in RPR titer after treatment were compared with those without a rise in titer. Earlier syphilis stage was the only variable significantly associated with an increase in RPR titer after therapy(Table 1). Age, gender, treatment regimen, ethnicity (Malagasy vs. non-Malagasy), prior syphilis, and Jarisch–Herxheimer reaction were not significantly associated with an increase in RPR titer during the 14 days after treatment.

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To our knowledge, these data represent the first systematic analyses of RPR increases in humans immediately after therapy of early syphilis. We found that initial RPR titers underestimate the maximal RPR titer in about 20% of early syphilis patients after therapy. In particular, earlier stage is associated with an increase in RPR titer, whereas age, gender, ethnicity, treatment regimen, prior syphilis, or a Jarisch–Herxheimer reaction were not significantly associated. Using the RPR titer measured at the time of treatment as the baseline to assess serologic response resulted in reclassification of approximately 3% of patients, slightly underestimating cures and overestimating failures.

Although we acknowledge the relatively limited clinical implications, our study quantifies the frequency of increase in RPR titers in the weeks immediately after early syphilis therapy. Although the Centers for Disease Control and Prevention Sexually Transmitted Diseases Treatment Guidelines recommend follow-up of nontreponemal serologic tests of syphilis patients at 6 and 12 months after therapy,3 from time to time, patients have repeat syphilis testing before these specified times. In our experience, this situation can result in confusion about the appropriate next step. Our data suggest that a rise in RPR titer within the 14 days after early syphilis therapy is not indicative of increased risk of treatment failure and does not require additional therapy or change in management.

We acknowledge several study limitations. Combining the azithromycin and penicillin treatment arms raises concern for possible effects; however, our analysis did not reveal a significant effect on RPR titer increase. We also acknowledge that in clinical settings where syphilis patients are tested repeatedly, RPR or Venereal Disease Research Laboratory test titers may vary ± 1 dilution. We sought to minimize variability by testing all serum simultaneously in a single laboratory. Nonetheless, some of the observed variations may reflect the acknowledged error of the test. We also excluded pregnant or HIV-positive patients, limiting the generalizability to these groups. We collected data regarding treatment response up to 6 months; it is conceivable that outcomes may have differed, if additional data were collected past that time point. Finally, as only patients with early syphilis were enrolled, these findings are not applicable for patients with late stages of syphilis.

These data also have implications for the research setting. Given that RPR titers increase in about 20% of participants with early syphilis, testing several times during the 2 weeks immediately after therapy will provide the most accurate peak titer for subsequent assessment of response to therapy. Had the initial RPR at time of treatment been used as the baseline for therapeutic response at 6 months, approximately 3% of patients treated would not have met criteria for serologic cure.

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