Syphilis Testing

November 21, 2024

Syphilis Testing

by Caitlin Legros, MSN, CNM

Fourteen years into my practice, and I still feel that familiar sinking feeling in my stomach when I see a positive Syphilis test. This time, my patient’s RPR came back positive, and the TP load was at 4. Time to look that up again—it’s one of those details that just never seems to stick! I remember the last time I had to call our Infectious Disease doctor to nail down the treatment plan. It’s not uncommon around here; many of our patients have a history of Syphilis.

Just this year, I experienced the unusual situation of seeing an active chancre infection for the first time in a patient. It presented as a wet, round ulcer on the vagina—not exactly your typical skin irritation. This painless ulcer is a hallmark of primary Syphilis. Most often, though, I see patients in the latent stage—a positive blood test but no visible lesions. Then there’s secondary Syphilis, characterized by a more widespread rash and swollen lymph nodes, and of course, tertiary Syphilis, which can be devastating, affecting the brain. I can’t help but think of artists like Degas, who sadly suffered from the effects of this disease.

Back to the clinic: a positive RPR is pretty routine here. There’s a chance of getting a false positive, especially among patients with risks such as HIV, IV drug use, or certain autoimmune conditions. So, the real challenge is figuring out if this is a new infection or if it’s been lurking undetected. Normally, I can evaluate lab results in under 30 seconds, so this one takes a minute longer than I’d like. Plus, there’s the pressure since the patient is already anxious to know if they need treatment again. A quick check on the CDC’s website usually clarifies things—just a couple of minutes and I’m on my way to being certain about the TP titer, which helps differentiate between new and old infections. Syphilis is caused by the bacterium Treponema Pallidum, which is a spirochete that twists around in a unique manner. And believe it or not, you can’t see it under a regular microscope without a special preparation called “dark field microscopy.” As a Microbiology nerd, it’s a bit of a bummer that I’ve never laid eyes on it!

The CDC reminds me that we need two tests to nail down a diagnosis: a non-treponemal screening test like the RPR and a diagnostic treponemal test. The RPR serves as a screen, while the treponemal test nails down whether the bacteria are definitely present. What’s interesting is that non-treponemal test titers tend to decrease over time with effective treatment, confirming that the bacterial burden is going down. Given the rising trend of Syphilis infections over the years, it’s no wonder that screening is mandatory for anyone admitted to the hospital for any reason. I first noticed this trend in Baltimore, where we had some of the country’s highest rates of new Syphilis infections at the time.

Primary infections can often be asymptomatic, and many of my patients deal with the social determinants of health that put them at risk, like poverty and systemic racism. While in Baltimore, I worked in an HIV/OB clinic, where many of my pregnant patients were infected with HIV as babies from their moms. Interestingly, while HIV is less common than Syphilis, it’s usually the test we order more frequently in the U.S. Unfortunately, congenital Syphilis has nearly quadrupled between 2015 and 2019. Clearly, we’re not hitting the screening levels we need, even when it’s mandated in many states during the first trimester. The rates for adult women aged 15-44 show a similar rise, jumping by 172% during that period. We’re seeing infection rates for Syphilis that we haven’t encountered since the 1950s, with over a million cases of congenital Syphilis worldwide every year.

Looking back, I never encountered a case of congenital Syphilis in my clinical practice, but that doesn’t mean it wasn’t there. My patients had plenty of risk factors—having multiple partners, struggles with substance abuse, unstable housing, and inconsistent prenatal care. It’s all too easy to miss screenings, especially when patients arrive in crisis without having had their labs drawn previously. Congenital Syphilis is serious; it can lead to fetal and neonatal death, prematurity, and low birth weight. Babies born with Syphilis can also exhibit noticeable physical signs, such as skeletal abnormalities and facial swelling. Checking for Syphilis is part of our routine lab work for fetal deaths.

Universal Syphilis testing is recommended and mandated in many states. All pregnant patients should get tested for Syphilis at least once during their first trimester, regardless of their background. It’s an invaluable opportunity for education and awareness about this easily preventable and treatable infection.