To the Editor: In Victoria from 2000 to 2006, infectious syphilis notifications (primary, secondary and early latent infections) increased about 25-fold from 0.2 cases per 100 000 population in 2000 to 4.7 cases per 100 000 population in 2006.1 The number of new diagnoses of HIV has also increased since 2004.1 After observing a few patients presenting with both syphilis and a concurrent new HIV diagnosis, we investigated the association of the two diseases using retrospective laboratory data. As the Victorian Infectious Diseases Reference Laboratory (VIDRL) incorporates the state HIV reference laboratory and also acts as the reference laboratory for syphilis serological testing, it was possible to identify the HIV status and/or time of HIV diagnosis of 85% of patients identified with infectious syphilis, based on syphilis serological findings and polymerase chain reaction testing as previously described.2

Three hundred and forty-seven male patients fulfilled the criteria for infectious syphilis in the period 1 January 2000 to 30 December 2006. This represents 68% of all patients with infectious syphilis notified to the Victorian Department of Human Services over the period. Within the group of 347 patients, there were 310 with a single episode of Treponema pallidum infection, of whom 44.5% were HIV-positive.

Thirty-seven patients were reinfected with syphilis, including 21 with their first episode recorded since 2000, and 11 with a serological pattern consistent with old treated syphilis recorded before reinfection during the study period. Of the 37 patients, 33 (of whom 23 were HIV-positive) had a second recorded episode and four (of whom three were HIV-positive) had a third recorded episode within the study period. Overall, 70.3% of patients with multiple episodes of syphilis were infected with HIV. Twenty patients presented with a concurrent diagnosis of infectious syphilis and previously un-diagnosed HIV infection. The trend over time is shown in the Box.

Several international studies have highlighted the disproportionate incidence of syphilis in patients infected with HIV in recent years. There is now good evidence that syphilis and HIV act synergistically with regard to both transmission and progression of both diseases.3-5 The above data clearly demonstrate the strong association between HIV infection and infectious syphilis in Victoria, and this trend continued in the first half of 2007. Given the more frequent syphilis reinfections observed in the HIV-infected group, it indicates persons with HIV form a potential reservoir for syphilis infection in this state. We would strongly recommend that any patient presenting with possible syphilis or HIV infection in Victoria or elsewhere in Australia should be tested for both diseases.

Episodes of infectious syphilis in Victoria by year of infection and HIV status

* Patients with evidence of prior syphilis infection at an unknown time.