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Syphilis and Human Immunodeficiency Virus (HIV)-1 Coinfection: Influence on CD4 T-Cell Count, HIV-1 Viral Load, and Treatment Response

Kofoed, Kristian MD*†; Gerstoft, Jan MD, DMSc; Mathiesen, Lars R. MD, DMSc; Benfield, Thomas MD, DMSc

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Sexually Transmitted Diseases: March 2006 - Volume 33 - Issue 3 - p 143-148
doi: 10.1097/01.olq.0000187262.56820.c0
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SYPHILIS IS AN ENDEMIC sexually transmitted disease. Several outbreaks of syphilis in North American and European cities have been reported recently, and the majority of outbreaks were among men who have sex with men. Of particular concern are the high rates of human immunodeficiency virus (HIV) infection in this population because this may be associated with an increased risk of concomitant transmission.1–6

Presence of sexually transmitted diseases, in particular sexually transmitted diseases with ulcers, facilitates sexual transmission of HIV-1 because the epithelial and mucosal barriers are disrupted.7–9 Further adding to the concern of cotransmission is a recent study that demonstrated increased HIV-RNA plasma levels during syphilis infection.10

A recent outbreak of syphilis in Copenhagen gave us the opportunity to study a cohort of patients with HIV-1 and syphilis coinfection. Here, we describe the effects of coinfection on rapid plasmin reagin (RPR), HIV-RNA viral load, CD4 cell count, and response to treatment of the syphilis infection.

Materials and Methods

Cases of syphilis diagnosed in HIV-infected patients between June 2003 and May 2004 at the Departments of Infectious Diseases at either Hvidovre University Hospital (HH) or Copenhagen University Hospital (RH) were included. All HIV-infected patients were screened for syphilis by serology during 5 months (November 15, 2003, through April 15, 2004) at HH and for the entire study period at RH. Additionally, patients suspected of syphilis and partners to infected patients were tested. Primary-stage syphilis was defined as having a dark field-positive lesion regardless of seroreactivity. Secondary syphilis was defined as seroreactivity and typical symptoms of the secondary stage of the disease (e.g., rash). Early latent syphilis was defined as syphilis characterized by seroreactivity without other evidence of disease and of known duration of less than 1 year. Late latent and latent syphilis of unknown duration were defined as syphilis characterized by seroreactivity without other evidence of disease and of known duration of more than 1 year or of unknown duration. Cure was defined as resolution of all signs and symptoms of syphilis and either a RPR titer of zero or a ≥fourfold decrease in RPR titer.

HIV-RNA, CD4 T cell counts, and RPR-serology were measured by standard methods before, during, and after an episode as described below. In both departments, the Ultra Sensitive method (Roche Molecular Systems, Branchburg, NJ) was used to determine HIV-RNA levels. The analyses were performed in real time with a lower limit of detection of 20 copies/ml. For samples recorded as below, the detection limit we assigned the value 19 copies/ml. At HH, viral loads greater than 150,000 copies/ml are not diluted further and are reported as greater than 150,000 copies/ml. The “before,” “during,” and “after” periods for analyses were defined as follows: “Before” was defined as 3 to 9 months before syphilis diagnosis, “during” was defined as the time of syphilis diagnosis (−2 to +2 weeks), and “after” was defined as 3 to 9 months after start of syphilis treatment.


Results are reported as median, direction of change, and mean and median change. Paired data before, during, and after syphilis infection are compared with the Wilcoxon signed rank test. Intrapatient comparisons were performed using nonparametric analysis of variance (Friedmans' 2-way ANOVA). Unpaired comparison was done using Fisher exact test.

A P value is considered significant at 0.05.


Approximately 2200 HIV-infected patients are followed on a regular basis at the 2 departments. In the study period, 41 patients had positive syphilis serology; of these, 2 patients had no “before” or “after” values, and 1 was lost to follow-up and had no measurement of HIV-RNA viral load at the time of diagnosis. Three patients were diagnosed with HIV-1 at the same time as the diagnosis of syphilis infection; therefore, they had no measurement of viral load and CD4 count before syphilis infection. This left 37 patients with “before-during-after” CD4 counts and viral loads, 38 patients with “before-to-during” CD4 counts, 37 patients with “before-to-during” viral load, and 40 patients with “during-to-after” CD4 counts and viral load.

All patients were newly diagnosed with syphilis. Seven patients had previously received treatment for syphilis. We had access to these patients' WR and RPR levels during and after their previous infections. All 7 returned to undetectable WR and RPR before they were diagnosed with syphilis and included in the current study.

The 41 patients had a median age of 41 years (range, 20–61), and 40 were men. The 1 woman immigrated to Denmark just before being diagnosed with syphilis and HIV-1 infection and was believed to have been infected in her country of origin. Of the men, 12 were of non-Danish origin; 22 were assumed to have been infected in Denmark. All patients reported men as their sexual partners.

Treatment with doxycycline tablets (100 mg twice daily for 14 days), procaine-penicillin G (1.2 million international units [MIU] intramuscularly qd × 10 days) or benzathine-benzylpenicillin (2.4 MIU intramuscularly weekly × 3) was offered at the discretion of the treating physician.

Of the 16 patients treated with penicillin, 9 were treated with procaine penicillin and 7 with benzathine penicillin. Of the patients treated with benzathine penicillin, 3 were diagnosed as having late latent/unknown, 1 early latent, 2 secondary, and 1 primary stage syphilis at time of diagnosis.

During the study period, treatment failure was observed in 4 patients (3 doxycycline, 1 procaine-penicillin). Of these, 2 were initially diagnosed as having late latent syphilis and treated with doxycycline. They later developed symptoms of neurosyphilis (headache, confusion, and weakness of upper and lower extremities). Cerebrospinal fluid (CSF) evaluation showed no intrathecal synthesis of specific IgG or IgM antibodies but abnormalities with elevated protein levels and lymphocytosis. They were both treated with high-dose intravenous penicillin. One completely recovered after the treatment. The other patient partly recovered but later relapsed, and after ruling out other possible explanations, changes were believed to be caused by HIV infection per se and the patient fully recovered on combination antiretroviral therapy (cART). The remaining 2 patients with treatment failure (1 procaine-penicillin and 1 doxycycline) both had secondary-stage syphilis at time of diagnosis and were diagnosed as treatment failures because of a fourfold increase in RPR during the first 6 months of follow-up. Both were retreated with doxycycline and responded adequately to treatment.

Patients were classified according to the first treatment, leaving 25 patients treated with doxycycline and 15 with penicillin for analysis.

Nine patients had CSF evaluation preformed. Four patients had central nervous system (CNS) symptoms, whereas the remaining 5 patients had CSF evaluation performed because of latent syphilis of unknown duration. No patients had intrathecal synthesis of specific IgG or IgM antibodies.

At the time of diagnosis, 17 (41%) patients had symptoms of secondary syphilis. Symptoms of primary syphilis were reported in 3 patients. There was an overrepresentation of doxycycline-treated patients in the primary and secondary syphilis (P&S) group (number observed, 15; number expected, 12; P = 0.06). Of the 41 patients, 33 (83%) were on cART. The median duration of antiretroviral of any kind was 4 years (range, 0–8). Only 5 (13%) had a CD4 cell count of less than 350 cells/mm3 at the time of syphilis diagnosis.

The median time span for the 38 patients who had “before-to-during” CD4 counts was 125 days (range, 81–270), and the median time span for the 40 patients who had “during-to-after” was 165 days (range, 79–276).

CD4 cell counts showed a trend towards a decrease during infection among all patients but was only statistically significant in the P&S group (median decrease of 80 cells/mm3) and among patients who had a “before” CD4 cell counts of 500 cells/mm3 or more (median decrease of 75 cells/mm3) (Table 1). In the “during-to-after” interval, there was a significant increase in the overall group, with a median of 63 cells/mm3. A significant increase in CD4 cell count was observed in the P&S group, patients on cART, patients with a CD4 cell count of 500 cells/mm3 or more at the time of diagnosis, and among patients treated with doxycycline (Table 1). HIV-RNA viral loads in the “before-to-during” time span only increased significantly among patients with CD4 cell counts of 500 cells/mm3 or more and among patients with undetectable HIV-RNA levels before their diagnosis of syphilis. On the other hand, viral loads decreased in the “during-to-after” time span in the overall group, in the P&S group, in the group with undetectable HIV RNA, and in the group treated with doxycycline (Table 1).

Change in CD4 Cell Count and HIV-RNA Levels in Relation to Stage of Syphilis, Antiretroviral Use, Viral Load, CD4 Cell Count, and Anti-Treponemal Treatment

Statistical significance is maintained when the analysis of changes in HIV viral load and CD4 cell count is limited to the 37 individuals with “before,” “during,” and “after” measurements.

In 37 patients with “before-during-after,” the median “before-to-after” time span was 291 days (range, 193–444). In this group there was a nonsignificant trend towards an increase in CD4 cell count in the overall group, and especially in the group on cART. The “before-to-after” viral loads showed no tendency of increase or decrease (data not shown).

Table 2 shows medians and corresponding P values by 2-way ANOVA for the 37 patients that had both “before,” “during,” and “after” measurements of CD4 cells and HIV RNA. In regard to CD4 cell count, the median value “during” syphilis infection is lower in all groups except in the 4 patients not on cART. But the differences are only statistically significant in the group with early latent disease and the group on cART. Median viral load level was higher during syphilis infection in the overall group, in the P&S group, and in the group not on cART, but only statistically significant in the P&S group.

Median CD4 Cell Count and HIV-RNA Levels in Relation to Stage of Syphilis, Antiretroviral Use, and Antitreponemal Treatment in Patients With ‘Before’, ‘During’, and ‘After’ Measurements

Of the 40 patients, 22 patients had RPR titers 2 to 4 months posttreatment, and RPR were available from 28 patients 5 to 7 months posttreatment (several RPR titers were available for all 40 patients, but the time of follow-up was not the same in all patients). The median time span from RPR at treatment start to the last RPR available was 7 months (range, 4–13). The proportion of patients with serological response to therapy was smaller in the group with syphilis of more than 1 year of duration compared to the other groups but not statistically significant (P = 0.174 and 0.104, respectively). The serological respond rates for the two different treatments were the same (Table 3).

Serological Response to Therapy in Relation to Stage of Syphilis and Choice of Antitreponemal Treatment


In this report, we demonstrate that significant changes in HIV-RNA levels and CD4 cell counts occur during syphilis infection of HIV-1-infected men. Further, we show comparable response rates to therapy with penicillin and doxycycline.

It has long been suspected that increases in plasma viral loads occur during STDs as in infections such as pneumonia, influenza, tuberculosis, and other.11,12 Buschacz et al.10 and we have now demonstrated that this is the case. The implications of this are naturally that concurrent syphilis infection of an HIV-1-infected individual increases the risk of HIV transmission to a sexual partner. It is well documented that increased HIV-1 plasma viral load is correlated to increased risk of sexual HIV transmission.13 This, in conjunction with enhanced seminal viral load during concurrent STD infection,14–16 adds even further to the risk of HIV transmission.

Syphilis and HIV transmission could be significantly reduced by the use of condoms during sexual practice, but since the introduction of cART, unprotected sex with regular and casual partners has increased among gay men. The increase in unprotected sex has been linked to treatment optimism, and, in particular, the success of cART in reducing plasma HIV-RNA has led to an unfounded loss of fear of transmitting or being infected with HIV.17–19 This may in part explain the large number of patients on cART in this study. However, a low or undetectable level of plasma HIV-RNA may be associated with HIV-1 transmission,20 and every effort must be made to educate and increase HIV prevention through counseling and promotion of safe-sex practices. Among individuals infected with HIV-1 who have unprotected sex with other HIV-1 individuals, there is a risk of superinfection with other strains that may carry resistance mutations or may have other pathogenic properties.21

Information about the effect of syphilis on HIV progression is scarce. In general, the evidence of an effect of a transient increase in viral load on disease progression is lacking.7 High viral set points are associated with a more rapid decline in CD4 cell counts,22 and, although transient, an increase during syphilis may be associated with a permanent loss of CD4 cells. Of more concern is the risk of ART resistance mutations occurring during viral replication,23–25 but intermittent viremia has not been consistently associated with an increased risk of subsequent virologic failure.26–29 Our observations stress the importance of a careful evaluation of other reasons to viremia during ongoing cART because this may indicate a concurrent infection such as syphilis.

The fact that 83% of the 41 patients were already on cART severely limits the degree by which syphilis could potentially impact CD4 levels and viral load. On the other hand, it is interesting to note that most of the change in CD4 cell count was primarily observed only in patients with >500 CD4 cell count. Similarly, this was the only group that clearly had a demonstrable return to baseline with the rise in CD4 following treatment. This suggests that the effects of syphilis may be much more limited in patients who are more immunologically compromised.

In the patients who were followed for the whole study period, we saw a tendency towards an increase in CD4 cell counts and stable HIV viral loads. This is what we would expect because most patients in this study were on cART. Studies have shown that CD4 cell counts continue to increase in patients even after several years of viral suppression on cART.30,31

The evidence of how CD4 cell counts respond to syphilis infection in patients without HIV coinfection is scarce; a single study found that although they were within the range of the normal distribution of immunophenotypes, the percentages of CD4 cells were significantly lower than in the uninfected population.32

We expected to find similar responses in viral load and CD4 cell count in the 2 groups treated with penicillin or doxycycline, but our data showed a significant increase in CD4 cell count and a decrease in viral load in the group treated with doxycycline, whereas there were no difference in CD4 cell count and viral load in the group treated with penicillin. This may be due to the antiinflammatory properties of doxycycline, resulting in a faster reduction in the believed immune-stimulated activation of HIV-1 RNA reservoirs caused by the syphilis infection.33,34 A recent study by Zink et al.35 found that in an experimental simian immunodeficiency virus (SIV) model of HIV CNS disease, minocycline suppressed viral load in the brain and decreased expression of CNS inflammatory markers. The same study found that in vitro, minocycline inhibited SIV and HIV replication. Another possible explanation is the overrepresentation of patients with P&S-stage syphilis in the doxycycline group. The truncated HIV RNA values at HH, where most patients received penicillin, makes it impossible for our study to detect changes in viral loads above the level of 150,000 copies/ml in this group of patients. This might well influence our results.

From our observations, it appears that doxycycline is a reliable choice for treatment of primary, secondary, early, and late latent-stage syphilis in HIV coinfected, but as expected, treatment failures were observed both in our and other studies.36–38 Serological response to syphilis treatment should therefore be carefully monitored.

This retrospective case-series study is based on existing medical records and laboratory results. Only in a few patients test results for other STDs were available, but they were investigated if suspected. The time spans for “before-to-during” and “during-to-after” vary a great deal, and for some of the patients in the late latent group, the “before” values were measured at a time when the patients were already infected with syphilis; this weakens the “before-to-during” changes in this group. Because of this and because of the small sample size and low statistical power, we might have failed to detect some significant changes, whereas other significant changes might have arisen by chance alone. Our study was conducted in patients who were enrolled in an HIV care program in greater Copenhagen and only included 1 female. Therefore, the results might not be generalizable to all HIV- and syphilis-coinfected patients. The study design, the natural history of HIV infection, and the effect of cART might have led to overinterpretation of the impact of syphilis infection on CD4 cell counts and viral load. A randomized controlled trial of doxycycline versus penicillin in HIV-1- and syphilis-coinfected individuals would further enlighten the issues raised in this study and should address the optimal treatment monitoring CD4 cell counts, viral load, and RPR over a longer period.


Primary- and secondary-stage syphilis was associated with a decrease in CD4 cell counts and an increase in HIV-RNA levels. These levels returned to presyphilis levels or improved after treatment for syphilis. This points out the importance of a surveillance program for syphilis infection in HIV-infected patients and underscores the importance of continuing efforts to educate and inform HIV-infected patients about the importance of safe sex practice.


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