Syphilis is a universally distributed disease caused by the spirochete Treponema pallidum subspecies pallidum that has important health, social, and economic repercussions. The number of syphilis cases has been increasing in various European and North American cities since the second half of the 20th century.1,2 Men who have sex with men (MSM) account for much of this increase.3–6 A worryingly high proportion of MSM with syphilis are also infected with the human immunodeficiency virus (HIV).3,5,7 The reasons for this change of trend appear to be complex7 but include migratory movements, contacts between different population groups, changes in risky behaviors, the use of various drugs, and the decrease in safe sex practices in MSM that coincided with the introduction of antiretroviral (ARV) therapy.8 In 2011, 3522 cases of syphilis were reported in Spain, and the incidence of the disease was 7.6 cases per 100 000 inhabitants. The annual incidence of syphilis grew considerably between 2005 and 2011.2 The autonomous communities that reported the highest rates were Madrid (14.3 cases per 100 000 inhabitants), the Balearic Islands (11.6 cases per 100 000 inhabitants), and Asturias (10.9 cases per 100 000 inhabitants).2 The aim of our study was to describe the clinical and epidemiological characteristics of syphilis in MSM within the area of influence of our hospital and to compare these characteristics with those of heterosexual men.

During the study period, 323 cases of syphilis were diagnosed. In 161 cases (49.8%), the patient's sexual orientation was included in the clinical record: 55 patients (34.2%) were MSM and 106 (65.8%) were heterosexual. Of the heterosexual patients, 39 (36.8%) were men and 67 (63.2%) were women. Although there was some interannual variability, the number of syphilis cases diagnosed per year was relatively stable. The trend over time in the diagnosis of syphilis cases in MSM remained stable throughout the study period.

Our study allowed us to obtain an overview of the clinical and epidemiologic characteristics of syphilis infection in the MSM population in our area. The high percentage of patients coinfected with HIV in our case series was noteworthy, as was the number of reinfections. The clinical form diagnosed most frequently was late latent syphilis or syphilis of unknown duration, as would be expected in a population in which screening accounts for more than half of diagnoses. The high percentage of patients lost to follow-up was notable.

In recent years, the incidence of syphilis has increased worldwide1,10 and also in Spain2 and the Balearic Islands specifically. This increase in the incidence of syphilis has occurred mainly in HIV-infected people, particularly MSM.7 Although our study found a stable trend in diagnoses of syphilis in MSM, it must be noted that the study period—from 2005, when the CLIA method of syphilis screening became available, until 2013—was very short.

Most of the worldwide increase in the incidence of syphilis occurred in the late 1990s and the first years of the 21st century, with a linear increase continuing until the present day. This increase has coincided with the introduction of ARV therapy—which allows better control of HIV infection—and a consequent change in risky behaviors brought about by a false sense of protection against potential HIV-related clinical complications.11 In a series of 26 patients in Spain, inconsistent condom use and a larger number of sexual partners were found to be risk factors for syphilis in MSM.12

Because our study was conducted at a hospital—as opposed to a center dedicated exclusively to treating STIs—we have no specific data on risk behaviors. Approximately half of the MSM patients in our series were diagnosed clinically—a notable finding, as one would expect more cases to be diagnosed by screening in this high-risk group. This finding can probably be explained by the fact that the patients included in the analysis were evaluated in a hospital setting as opposed to a primary care center or a center dedicated exclusively to STIs, where screening would be the predominant diagnostic method.

When the MSM population was compared with the population of heterosexual men, the symptomatic forms of syphilis—primary, secondary, and neurosyphilis—were found to be more frequent in MSM, although the differences were not statistically significant. HIV coinfection was also more common in MSM. This finding is consistent with the previous literature,13 although, notably, the percentage of MSM coinfected with HIV was much larger than in other series,4,5,12 including a Spanish multicenter epidemiologic study of more than 500 MSM with syphilis.13 The high percentage of HIV coinfection in our case series—even higher than that found in a Spanish epidemiologic study of hospitalizations for syphilis3—was not limited exclusively to MSM. Because syphilis and HIV share mechanisms of transmission, diagnosis of both infections is not uncommon, especially in groups like MSM that engage in risky sexual practices. In addition, syphilis can enhance transmission of HIV, mainly through mucosal abnormalities caused by genital ulcers.14 The association between syphilis and HIV is therefore of great epidemiologic and clinical importance because both infections are associated with high morbidity and mortality and are therefore public health problems.7,8 HIV infection can also modify the natural course of syphilis infection, and symptomatic infections (secondary syphilis, neurosyphilis) are more common in HIV-infected patients.15 This could explain the larger number of symptomatic syphilis diagnoses in MSM in our study (nearly three quarters of MSM with syphilis were also infected with HIV). This result contrasts with the findings of other international case series in which the percentage of coinfected patients was smaller,16–19 although most of those works were based on studies of population screening.

Remarkably, nearly three quarters of the cases of HIV-syphilis coinfection were diagnosed simultaneously, a much higher percentage than that found in other case series.4,18,20 In these patients, HIV was diagnosed at a relatively early stage (with a median CD4 count of 456), as in previous studies.4 This finding highlights the importance of proper screening for HIV infection in syphilis-infected MSM, which could allow the viral infection to be diagnosed at an earlier stage.

The number of patients lost to follow-up in our study was high—approximately one third of the evaluated population—but lower than the percentage found in other case series.19

The percentage of MSM patients was lower than that found in other Spanish studies, although the earlier works were based on studies carried out in large cities at centers specialized in STIs, where larger aggregations of this risk group can be found.4,5,12

Our study had several limitations. As a retrospective review based on data from clinical records, it was subject to information bias. Additionally, the number of MSM patients was low, probably because many cases with positive serologies for syphilis were excluded from the analysis (latent and treated syphilis were indistinguishable in the patient records). In light of the fact that different societies21–23 have different recommendations regarding screening methods, one possible explanation for this—in addition to the lack of patient follow-up—could be an erroneous interpretation of serologic profiles. Finally, because sexual orientation was recorded in less than half of the clinical histories, a large number of patients were excluded from the analysis.

In conclusion, syphilis-HIV coinfection is very common, especially in the MSM population. The presence of syphilis or HIV should alert the physician to the possibility of the other infection. HIV screening in patients with syphilis, especially MSM, would probably lead to more, and earlier, diagnoses of HIV.

The authors declare that they have no conflicts of interest.