A retrospective study of the clinical features of new syphilis infections in an HIV-positive cohort in Alberta, Canada

Abstract

Objectives: Syphilis is a global health concern with an estimated 12 million infections occurring annually. Due to the increasing rates of new syphilis infections being reported in patients infected with HIV, and their higher risk for atypical and severe presentations, periodic screening has been recommended as a routine component of HIV care. We aimed to characterise incident syphilis presentation, serological features and treatment response in a well-defined, HIV-infected population over 11 years.

Methods: Since 2006, as routine practice of both the Southern Alberta Clinic and Calgary STI programmes, syphilis screening has accompanied HIV viral load measures every 4 months. All records of patients who, while in HIV care, either converted from being syphilis seronegative to a confirmed seropositive or were reinfected as evidenced by a fourfold increase in rapid plasma reagin (RPR) after past successful treatment, were reviewed.

Results: We identified 249 incident syphilis infections in 194 different individuals infected with HIV; 72% were initial infections whereas 28% were reinfections. Half (50.8%) of the infections were asymptomatic and identified only by routine screening. Symptomatic syphilis was more common when RPR titres were higher (p=0.03). In patients with recurrent syphilis infection, a trend was noted favouring symptomatic presentation (62%, p=0.07). All 10 patients with central nervous system (CNS) syphilis involvement presented with an RPR titre ≥1:32. Following syphilis infection, a decline of 42 cells/mm³ in CD4 (p=0.004) was found, but no significant changes in viral load occurred. No association was found with the stage of syphilis or symptoms at presentation and antiretroviral therapy use, CD4 count or virological suppression.

Conclusion: Routine screening of our HIV-infected population identified many asymptomatic syphilis infections. The interaction of HIV and syphilis infection appears to be bidirectional with effects noted on both HIV and syphilis clinical and serological markers.

Keywords: epidemiology; public health.

Figure 1

Percentage of episodes of syphilis diagnosed based on symptoms in a HIV-infected population.

Figure 2

Percentage of syphilis episodes divided by symptom at presentation based on initial rapid plasma reagin (RPR) titre. Individuals who had symptoms compared with those that did not were more likely to have a higher initial RPR (p=0.0339). The most common symptoms were rash and ulcer/lesion with influenza-like illness, condylomata and lymphadenopathy being relatively rare. Those with neurological symptoms had a significant elevation of their initial RPR titres compared with all other symptoms (p=<0.001) and there were no cases of neurosyphilis with RPR titres less then 1:32 dilutions.

Figure 3

There is an increased number of incident syphilis infections among HIV-positive individuals who are active in care programmes from 2006 to 2016. There is an apparent trend of decreased proportion of late latent disease.

Figure 4

Scatter plot of CD4 count at syphilis diagnosis versus CD4 count at follow-up appointment after the treatment of syphilis. CD4 count was noted to decrease by an average of 42.2 cells/mm³ (p=0.004).

Figure 5

Scatter plot of viral load (adjusted on a logarithmic scale to account for wide variation in values) at syphilis diagnosis versus viral load at follow-up appointment after treatment of syphilis. Viral load was noted to increase by an average of 3.09 copies/mL in relation to syphilis coinfection (p=0.47).

Figure 6

The percentage of syphilis episodes comparing initial symptom presentation divided by recurrent infections. There is a trend demonstrating that individuals with recurrent syphilis infections were more likely to be symptomatic on presentation; however, this did not reach significance (p=0.0799).