Comparison of Early and Late Latent Syphilis -- Colorado, 1991

Latent syphilis (i.e., the presence of serological evidence for syphilis without clinical manifestations) is divided into early latent ({EL} less than 1-year's duration) and late latent ({LL} more than 1-year's duration) stages (1). LL syphilis, which is often associated with low nontreponemal test (e.g., rapid plasma reagin {RPR}) titers and is presumed to have been acquired in the distant past, is not routinely included in syphilis surveillance reports and analyses. Although a separate classification of "unknown latent syphilis" has been proposed (1), in practice, duration is unknown for nearly all syphilis cases that are classified as LL. This report compares EL and LL syphilis cases in Colorado during 1991 and demonstrates substantial overlap in their characteristics.

Colorado EL and LL syphilis cases reported in 1991 were abstracted for information on age, sex, racial/ethnic group, and serologic test results (RPR). Persons aged greater than or equal to 60 years with RPR titers less than or equal to 16 were not included among LL cases, because these are usually closed administratively without investigation by disease-control staff.

Serologic and demographic data were available for 33 (94%) of 35 EL and 92 (91%) of 101 LL cases reported in 1991. Females composed 17 (52%) EL and 35 (38%) LL cases. Blacks composed 13 (39%) EL and 28 (30%) LL cases; whites composed seven (21%) EL and 28 (30%) LL cases; Hispanics composed 30% of both EL and LL cases.

Of patients with EL syphilis, 27 (82%) had RPR titers greater than or equal to 8; 40 (43%) patients with LL syphilis also had RPR titers greater than or equal to 8 (Figure 1). The percentage of cases with RPR titers greater than or equal to 32 was 42% for EL and 18% for LL. The median age group was 25-29 years for EL and 30-34 years for LL patients. Of patients with EL syphilis, 28 (85%) were aged less than or equal to 39 years; 70 (76%) patients with LL syphilis were also in this age range (Figure 2). Based on the combination of both RPR titer greater than or equal to 8 and age less than or equal to 39 years, 32 (35%) patients with LL syphilis were similar to the majority of EL patients.

Reported by: KA Gershman, MD, HIV/STD Surveillance Program, RE Hoffman, MD, State Epidemiologist, Colorado Dept of Health. Clinical Research Br, and Surveillance and Information Systems Br, Div of Sexually Transmitted Diseases and HIV Prevention, National Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: The division of latent syphilis into early and late stages is based on treatment and public health considerations; a previous study of untreated syphilis indicated that most secondary relapses (mucocutaneous lesions) occurred during the first year after infection (2). In the United States, since the 1960s, the early latent stage has been defined as 1 year from the onset of infection. In practice, latent syphilis is classified as EL with evidence that a person acquired infection during the previous 12 months based on

1. a nonreactive serologic test for syphilis or a fourfold rise in titer from a previous serologic test for syphilis during the previous 12 months; 2) a history of symptoms consistent with primary or secondary syphilis without a history of treatment in the previous 12 months; or 3) a history of sexual exposure to a partner with confirmed or presumptive primary, secondary, or early latent syphilis and no history of treatment during the previous 12 months. If none of these criteria are met, a case of latent syphilis is classified as LL; the duration of infection is usually unknown.

Public health surveillance for syphilis is based on reported cases of primary and secondary (P&S) or early (P&S plus EL) syphilis. Because a substantial proportion of persons with infectious P&S syphilis do not seek medical attention despite symptoms (3), reporting that includes EL cases presumably reflects the true incidence of syphilis during the previous 12 months more accurately than does reporting of P&S syphilis alone. The findings in this report that the age and serologic titer patterns of LL and EL syphilis patients are similar suggest that a substantial number of LL case-patients may have acquired infection during the previous 12 months, even though information was inadequate to classify these cases as EL. Based on these findings, the actual number of EL cases in Colorado could be more than twofold greater than what is recognized.

Limitations in knowledge about the natural history of nontreponemal test titers in untreated syphilis precludes use of these tests to assess duration of infection. Although peak titers are reached during the first year of untreated infection, data on their rate and variability of subsequent decline are limited (4).

For monitoring morbidity trends and evaluating control programs, the category P&S syphilis may be optimal, especially when focusing on patients voluntarily seeking care with signs or symptoms (5). The detection of EL and LL syphilis cases is more dependent on active case-finding conducted by STD programs, including partner notification and serologic screening. Although the division of latent syphilis cases into EL and LL stages has been useful for treatment and partner notification, the findings in this report suggest this classification is problematic for use in surveillance.

References

1. CDC. Case definitions for public health surveillance. MMWR 1990;39(no. RR-13).

2. Sparling PF. Natural history of syphilis. In: Holmes KK, March PA, Sparline PF, Wiesner PJ, eds. Sexually transmitted diseases. New York: McGraw-Hill, 1990:214.

3. Brown WJ, Donohue JF, Axnick NW, Blount JH, Ewen NH, Jones OG. Syphilis and other venereal diseases. Cambridge, Massachusetts: Harvard University Press, 1970:41.

4. Hart G. Syphilis tests in diagnostic and therapeutic decision making. Ann Intern Med 1986;104:368-76.

5. CDC. Epidemic early syphilis -- Montgomery County, Alabama, 1990-1991. MMWR 1992; 41:790-4.

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