What is the diagnosis and treatment for a patient with a positive syphilis test, specifically a Rapid Plasma Reagin (RPR) titer of 1:2, who is asymptomatic and has no history of previous syphilis testing or treatment?

Diagnosis and Treatment of Asymptomatic Syphilis with RPR 1:2

This patient has late latent syphilis (or latent syphilis of unknown duration) and should be treated with benzathine penicillin G 2.4 million units IM once weekly for three consecutive weeks. 1, 2

Staging Rationale

Late latent syphilis is the appropriate classification because:

• The patient has no clinical signs or symptoms (asymptomatic) 1
• Positive serologic testing confirms infection (reactive treponemal test implied by positive syphilis test, with RPR 1:2) 1
• Last sexual exposure was "a few years ago," meaning infection occurred >12 months previously 1, 2
• No history of previous diagnosis or treatment 1

The CDC case definition for late latent syphilis specifically describes this scenario: latent syphilis where initial infection occurred greater than 1 year previously. 1 Since the patient's last sexual encounter was years ago and they have no symptoms, this definitively places them in the late latent category rather than early latent (which requires infection within the preceding 12 months). 1

Treatment Protocol

The standard treatment regimen is:

• Benzathine penicillin G 2.4 million units IM once weekly for 3 consecutive weeks (total 7.2 million units) 1, 2, 3

This three-dose regimen is required for late latent syphilis, in contrast to the single-dose regimen used for primary, secondary, or early latent syphilis. 1, 2

Important Clinical Considerations

The low RPR titer (1:2) is consistent with late latent disease:

• In late latent syphilis, RPR sensitivity drops to 61-75%, and 25-39% of late latent cases have non-reactive RPR 2
• Only 41% of late latent cases have titers >1:8 1
• Low titers are expected in late-stage infection as nontreponemal antibodies decline over time 3

HIV testing is mandatory:

• All patients diagnosed with syphilis must be tested for HIV infection 2, 3
• HIV-infected patients with late latent syphilis require CSF examination to rule out neurosyphilis 1
• HIV-infected patients need more frequent monitoring (every 3 months instead of 6 months) 1, 2

Follow-Up Monitoring

Serologic follow-up schedule:

• Clinical and serologic evaluation at 6,12, and 24 months after treatment 1, 2
• Use the same nontreponemal test (RPR) at the same laboratory for all follow-up testing 2, 3
• Expect minimal serologic response in late latent disease—many patients remain "serofast" with persistent low titers 2

Treatment failure indicators:

• Clinical signs or symptoms that persist or recur 1, 2
• Sustained fourfold increase in nontreponemal titer 1, 2
• Failure to achieve fourfold decline in titer within 12-24 months (though this is less reliable in late latent disease) 4

Common Pitfalls to Avoid

Do not undertreate based on the low titer:

• The RPR of 1:2 does not indicate less severe disease or justify single-dose therapy 1, 2
• Late latent syphilis always requires three weekly doses regardless of titer 1, 2

Do not misclassify as early latent:

• The timing of last sexual exposure (years ago) definitively excludes early latent classification 1
• Early latent requires documented infection within 12 months 1

Do not use alternative antibiotics without compelling reason:

• Penicillin remains the only proven effective treatment for late latent syphilis 1, 4
• If penicillin allergy exists, desensitization is preferred over alternative regimens 1, 2
• Doxycycline or other alternatives have limited evidence in late latent disease 1