Syphilis is a sexually transmissible infection (STI) caused by the spirochete Treponema pallidum. It has re-emerged as an important STI especially with the introduction of pre-exposure prophylaxis for HIV (PREP) and condomless sex.
We spoke with Dr Melanie Bissessor from Melbourne Sexual Health Centre about the challenges clinicians face when managing syphilis – and strategies for overcoming them.
Dr Bissessor: “The biggest clinical challenge is deciding whether a patient actually has syphilis: syphilis is not called the “great mimicker” lightly. The rash of secondary syphilis is highly variable in appearance and may be mistaken for other common dermatological conditions such as psoriasis, pityriasis rosea and viral exanthems.
“Pathognomonically, the rash affects the palmar and plantar surfaces. A chancre, which is the hallmark of primary syphilis, usually appears as a solitary painless ulcer but may be multiple or painful and may resemble genital herpes in especially HIV positive individuals. To add to the dilemma, if untreated, syphilis infection may enter a period of latency where there are no symptoms or signs of infection, but the patient is still infectious.”
How does a clinician overcome this clinical challenge?
Dr Bissessor: “The best way to is always have a high index of suspicion that the patient with these signs and symptoms may have syphilis, especially if the patient belongs to a high-risk group. These include but are not limited to men who have sex with men, sex workers and people who inject drugs.
“Consequentially, swabbing the genital ulcer or skin lesion and testing for Treponema pallidum using PCR (TP PCR) methods as well as ordering syphilis serology will make the diagnosis much clearer. As mother-to-child transmission of syphilis can result in devastating outcomes for the newborn, women should be screened routinely for syphilis.”
The other diagnostic challenge that clinicians face is interpreting the syphilis serology.
Dr Bissessor: “The mainstay of diagnosis of syphilis is serological testing. Serological tests for syphilis are grouped as: specific (treponemal) and nonspecific (nontreponemal).
“Specific treponemal serological tests for syphilis include: TPPA or TPHA; FTA-Ab and EIA. These tests confirm the diagnosis of syphilis, but do not indicate whether the disease is active or cured, and often remain reactive for years after effective therapy. When a patient has syphilis, this specific serology usually remains positive for the rest of their lives.
“Non-specific, non-treponemal serological tests for syphilis include: the RPR test, and venereal disease research laboratory (VDRL) test. The RPR titre should be repeated on the day of treatment and at three, six, and 12 months after treatment as part of STI testing. A fourfold drop in titre from the day of treatment (for example: from 1:32 to 1:8) at six months following treatment is indicative of an adequate response to treatment. A new infection in a patient who has had syphilis in the past is indicated by a fourfold rise in RPR titre from baseline (for example: from 1:4 to 1:16).”
Clinicians are sometimes unsure whether a patient requires a stat dose of 1.8 g of benzathine penicillin or needs weekly benzathine penicillin over three weeks.
Dr Bissessor: “The stage of syphilis determines the treatment regimen to be given. The presence of physical symptoms and signs of syphilis with a positive TP PCR implies early infectious syphilis and requires just a stat dose of benzathine penicillin.
“Additionally, if a patient has had recent syphilis serology in the last two years with documented treatment and now has a fourfold rise in RPR titre, then this patient requires just a stat dose of benzathine penicillin as the infection is classified as early.
“In the absence of the clinical features of syphilis or previous documented treatment or serology in the last two years, then the patient requires weekly benzathine penicillin over three weeks. If in doubt, give weekly benzathine penicillin over three weeks.”
GPs see a range of patients for diverse conditions and sometimes STI testing is not considered unless a patient asks for it.
Dr Bissessor: “Opportunistic STI screening at the time of other clinical presentations, such as patients presenting for routine immunisations or repeat prescriptions for their chronic medical conditions, will help increase testing rates of STIs and increase a doctor’s confidence to test and interpret STI results.
“STI testing is easy to incorporate in our practice and access to the Australasian Society for HIV, Viral Hepatitis and Sexual Health Medicine guidelines or the dedicated Melbourne Sexual Health Centre doctors helpline for STI advice will assist with further management of more difficult STI cases.”