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Syphilis, primary
2026 Case Definition

Syphilis, primary
2026 Case Definition
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NOTE: A surveillance case definition is a set of uniform criteria used to define a disease for public health surveillance. Surveillance case definitions enable public health officials to classify and count cases consistently across reporting jurisdictions. Surveillance case definitions are not intended to be used by healthcare providers for making a clinical diagnosis or determining how to meet an individual patient’s health needs.

Subtype(s)

  • Syphilis
  • Syphilis, secondary
  • Syphilis, early non-primary non-secondary
  • Syphilis, unknown duration or late
  • Syphilis, congenital

Background

A stage of infection with Treponema pallidum characterized by the presence of a chancre or chancres at the site(s) of inoculation.

Clinical Criteria

In the absence of a more likely alternative diagnosis, meets at least one of the following signs:

  • One or more ulcerative lesions (i.e., chancre), which may differ considerably in clinical presentation, OR
  • Syphilitic balanitis of Follmann.

Laboratory Criteria

Confirmatory Laboratory Evidence:

Meets at least one of the following criteria:

  • Direct detection of T. pallidum by darkfield microscopy in a specimen that was both not obtained from the oropharynx and not potentially contaminated by stool, OR
  • Direct detection of T. pallidum by immunohistochemistry (IHC) staining in a specimen that was both not obtained from the oropharynx and not potentially contaminated by stool, OR
  • Direct detection of T. pallidum by nucleic acid amplification test (e.g., polymerase chain reaction [PCR], loop-mediated isothermal amplification [LAMP]) or a diagnostically equivalent molecular method in any specimen.

Presumptive Laboratory Evidence:

Meets at least one of the following criteria:

  • A current (i.e., a test performed in the context of this index presentation) reactive blood-based nontreponemal antibody (lipoidal antigen-based) test (i.e., Venereal Disease Research Laboratory [VDRL], rapid plasma reagin [RPR], point-of-care, or equivalent nontreponemal method), OR
  • A current (i.e., a test performed in the context of this index presentation) reactive blood-based treponemal antibody test (i.e., T. pallidum particle agglutination [TP-PA], enzyme immunoassay [EIA], chemiluminescence immunoassay [CIA], multiplex flow immunoassay [MFI or MIA], fluorescent treponemal antibody-absorption [FTA-ABS], point-of-care, or equivalent treponemal method).

Note: The categorical labels used here to stratify laboratory evidence are intended to support the standardization of case classifications for public health surveillance. The categorical labels should not be used to interpret the utility or validity of any laboratory test methodology.

Case Classification

Probable

  • Meets clinical criteria AND meets presumptive laboratory evidence.

Confirmed

  • Meets clinical criteria AND meets confirmatory laboratory evidence.

Related Case Definition(s)

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Last Reviewed: June 2, 2026
Source: Office of Public Health Data, Surveillance, and Technology