In this series, syphilis infection was associated with a significant increase in HIV VL in 28.0% of patients and a decrease in CD4 cell count, which was greater among those patients with a better immunologic status.
The conjunction of syphilis and HIV infections may have important epidemiologic and clinical consequences. A worrisome finding in our series, which is in line with other studies,17 is that more than two thirds of the syphilis cases were diagnosed in previously known HIV-infected patients, many of whom were on HAART, which highlights the risky behavior of our patients and the weak preventive strategies.
Increases in plasma HIV VL during sexually transmitted diseases and other infections have long been reported.12-14,18,19 In agreement with 2 recent studies,15,16 we confirm that this is also the case in patients who are coinfected with HIV and syphilis. It has been suggested that increases in HIV VL occur mainly in patients with secondary syphilis.12,13,15 In our study, there was no difference in the virologic change, depending on the stage of syphilis. Although a considerable proportion of previously suppressed patients who were on HAART had a detectable VL during syphilis, the only factor associated with an increase in HIV VL was not being on HAART. In line with data reported in several studies of HIV-infected patients with coinfections,12,15 we found no reduction in VL after syphilis treatment. These findings may be related to persistent immune activation.12,13
Concerning CD4 cell changes during follow-up, syphilis infection was clearly associated with a decrease in CD4 cell count, as has also been reported by others.15,16 The fact that more than one half of our patients were on HAART may have limited the degree of the impact of syphilis on CD4 cell levels. Nevertheless, we observed that CD4 cell counts decreased in HIV patients on HAART and in those not on HAART. Kofoed et al16 suggested that the effects of syphilis may be much more limited in patients who are more immunologically compromised. In our series, most patients were quite well maintained immunologically and the CD4 cell count decreased in the series overall. In agreement with Kofoed et al,16 however, we did observe a greater CD4 cell count decrease among patients with a higher baseline CD4 cell count, and in addition, the only factor associated with a CD4 decrease >100 cells/μL was the CD4 cell count before syphilis. As expected, patients on HAART who were followed for the whole study period demonstrated an increase in their CD4 cell count after syphilis treatment.
We acknowledge that our study has certain limitations, such as its retrospective design and the lack of a control group of HIV patients not infected with syphilis. The VL and CD4 cell measurements also were occasionally missing at some time points of the study. Conversely, we need to highlight that the study included a large sample of patients. As far as we are aware, ours would be the third and largest study to date to evaluate the impact of syphilis infection on HIV VL and CD4 cell counts. In addition, ours is the only study that analyzes factors associated with changes in HIV VL and CD4 cell count during syphilis.
In summary, syphilis infection in HIV-infected patients was associated with a significant decrease in CD4 cell count and an increase in plasma HIV VL. Our data also confirm the information provided by recent epidemiologic studies of syphilis outbreaks among men who have sex with men. Integrated public health efforts to prevent new syphilis infections and to identify and treat affected patients as soon as possible are therefore warranted to reduce the spread of both diseases within this population.
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