Background:

Syphilitic ulcers are known to facilitate the transmission of HIV infection, but the effect of syphilis infection on HIV viral loads and CD4 cell counts is poorly understood.

Methods:

We abstracted medical records for HIV-infected male syphilis patients seen at three clinics in San Francisco and Los Angeles from January 2001 to April 2003. We compared plasma HIV-RNA levels and CD4 cell counts during syphilis infection with those before syphilis infection and after syphilis treatment, using the Wilcoxon signed rank test.

Results:

Fifty-two HIV-infected men with primary or secondary syphilis had HIV viral load and CD4 cell count data available for analysis; 30 (58%) were receiving antiretroviral therapy. Viral loads were higher during syphilis compared with pre-syphilis levels by a mean of 0.22 RNA log 10 copies/ml (P= 0.02) and were lower by a mean of− 0.10 RNA log 10 copies/ml (P= 0.52) after syphilis treatment. CD4 cell counts were lower during syphilis infection than before by a mean of− 62 cells/mm 3 (P= 0.04), and were higher by a mean of 33 cells/mm 3 (P= 0.23) after syphilis treatment. Increases in the HIV viral load and reductions in the CD4 cell count were most substantial in men with secondary syphilis and those not receiving antiretroviral therapy.

Conclusion:

Syphilis infection was associated with significant increases in the HIV viral load and significant decreases in the CD4 cell count. The findings underscore the importance of preventing and promptly treating syphilis in HIV-infected individuals.