Syphilis, unknown duration or late
2026 Case Definition

Background

A stage of infection with T. pallidum characterized by no clinical signs or symptoms of primary or secondary syphilis and either the infection occurred greater than 12 months prior or there is insufficient evidence to conclude that infection was acquired during the previous 12 months.

Clinical Criteria

• Documented history of syphilis.

Laboratory Criteria

Confirmatory Laboratory Evidence:

• Direct detection of T. pallidum by 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., PCR, LAMP) or a diagnostically equivalent molecular method in any specimen.

Presumptive Laboratory Evidence:

• A current (i.e., a test performed in the context of this index presentation) reactive blood-based nontreponemal antibody test (i.e., VDRL, RPR, point-of-care, or equivalent nontreponemal method), AND
• A reactive blood-based treponemal antibody test (i.e., TP-PA, EIA, CIA, MFI or MIA, FTA-ABS, point-of-care, or equivalent treponemal method)^¶.

Supportive Laboratory Evidence:

• A current (i.e., a test performed in the context of this index presentation) blood-based nontreponemal antibody test titer demonstrating a fourfold or greater increase^§§ AND
• No evidence of a concurrent nonreactive blood-based treponemal antibody test.

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.

^¶Current or historical reactive treponemal antibody tests can be used to satisfy this criterion.

^§§For surveillance purposes, there is no requirement that the blood-based nontreponemal antibody test be repeated. However, in the absence of treatment initiation, when blood-based nontreponemal antibody testing is repeated, if the repeat specimen is collected less than or equal to 30 days after the specimen that demonstrated a fourfold increase in titers, and the repeat specimen demonstrates that the fourfold increase in titers was not sustained, the case does not meet the supportive laboratory evidence for unknown duration or late syphilis.

Probable

• No evidence of having acquired the infection within the preceding 12 months^*** AND does not meet clinical criteria AND meets presumptive laboratory evidence, OR
• No evidence of having acquired the infection within the preceding 12 months^*** AND meets clinical criteria AND meets supportive laboratory evidence, OR
• Does not otherwise meet the surveillance case definition for any other stage of syphilis as described above AND no evidence of having acquired the infection within the preceding 12 months^*** AND meets the definition for likely or verified neurologic, ocular, otic, or late clinical manifestations of syphilis as described later in this position statement.

Confirmed

• No evidence of having acquired the infection within the preceding 12 months^*** AND meets confirmatory laboratory evidence.

^***See epidemiologic linkage criteria and other evidence of infection acquired during previous 12 months in Syphilis, early non-primary non-secondary case definition.

• Syphilis (Treponema pallidum) | 2026 Case Definition