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Prevalence Monitoring in Syphilis Surveillance: Results From a Multicenter Research Program

FINELLI, LYN DrPH*; FARLEY, THOMAS P. MD; GIBSON, JAMES J. MD; LANGLEY, CAROL MD§; HWANG, LU-YU MD; LEVINE, WILLIAM C. MD*

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Background Syphilis seroprevalence data can be used as an independent measure of syphilis trends and to augment syphilis case report data for program planning. The prevalence of reactive syphilis serology in jails, delivery rooms, and drug treatment centers was examined from 1995 to 1999. Prevalence was evaluated by age and gender at each site and compared with county primary and secondary syphilis case rates. Annual prevalence of high titer–reactive serology in jails was compared with primary and secondary syphilis case rates.

Goal The goal was to examine trends in syphilis seroprevalence and to evaluate the relationship of trends in seroprevalence to reported cases.

Study Design This was a cross-sectional survey.

Results Prevalence of reactive serology and high titer–reactive serology was lowest among women in delivery rooms (2.9% and 0.4%, respectively) and highest among women in jails (11.1% and 4.1%, respectively), indicating substantial recently treated or active infection among women in jails. Trends in high titer–reactive serology were similar to primary and secondary syphilis case rates.

Conclusion The prevalence of high titer–reactive serology can provide valuable information about community syphilis morbidity for use in prevention and control programs.

Syphilis seroprevalence data were gathered from jails, delivery rooms, and drug treatment centers in four sites over 5 years. Seroprevalence is highest among women in jails and lowest in women in delivery rooms. Syphilis seroprevalence trends were similar to trends in syphilis case rates; seroprevalence data can be used as an adjunct to case reports for syphilis program planning.

From the *Centers for Disease Control and Prevention, Atlanta, Georgia; †Louisiana Department of Health and Hospitals, New Orleans, Louisiana; ‡South Carolina Department of Health and Environmental Control, Columbia, South Carolina; §Mississippi State Department of Health, Jackson, Mississippi; and ∥University of Texas Health Sciences Center, Houston, Texas

The authors thank those people without whom this study could not have been undertaken: Virginia Andrews, Susan Bradley, Jim Braxton, Melinda Flock, Jan Risser, Richard Kahn, Blake Lloyd, Kera Mosley, Dan Rosenberg, Maya Sternberg, and Jo Valentine.

Correspondence: Lyn Finelli, DrPH, MS, Epidemiology Branch, Division of Viral Hepatitis, National Center for Infectious Diseases, MS G-37, Centers for Disease Control and Prevention, 1600 Clifton Road NE, Atlanta, GA 30333.

Received for publication October 23, 2001,

revised March 5, 2002, and accepted March 8, 2002.

PRIMARY AND SECONDARY (P&S) syphilis rates have been declining in the United States since the last national epidemic, which peaked in 1990. 1 Declines in P&S syphilis have been followed by repeated epidemics occurring approximately every 7 to 10 years. 1 During 1960 to 1990, these cyclical epidemics resulted in progressively higher peaks in morbidity. 2 In 1995, the Centers for Disease Control and Prevention funded a 5-year multisite research program entitled “Innovations in Syphilis Prevention: Reconsidering the Epidemiology and Involving Communities” (ISP). The purpose of the research program is to develop innovative strategies for the prevention and control of syphilis in collaboration with communities affected by syphilis, with special emphasis on the southern United States. 3

The initial phase of the project lasted 2 years and involved formative research evaluating epidemiologic, social, and behavioral factors associated with syphilis transmission and developing pilot interventions for the prevention and control of syphilis. The second phase of the program is ongoing and is focused on intervention implementation and evaluation.

The collection of syphilis seroprevalence data has spanned both phases of the project. The purpose of monitoring of syphilis seroprevalence is to evaluate trends in the prevalence of reactive serologic tests for syphilis over time in populations routinely screened. Seroprevalence data are independent of syphilis case reports and of the biases associated with case-reporting practices and can provide information about community syphilis-associated morbidity. The data presented here have been collected as part of the syphilis seroprevalence monitoring activity in the ISP project.

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Methods

From 1996 to 1999, demographic and serologic data were collected on persons with reactive and nonreactive nontreponemal tests for syphilis in each of four research centers (Hinds County, MS; East Baton Rouge Parish, LA; Orangeburg and Bamberg Counties, SC; and Harris County, TX) and one or more of three required types of testing sites: county jails, delivery rooms, and drug treatment centers. Records were excluded from the analysis if they were missing combinations of date of birth, race/ethnicity, and date and results of serologic tests. Serologic test reactivity was calculated by dividing the number of reactive serologic tests for syphilis by the total number of tests for syphilis (denominator includes only valid tests) and is expressed as a percentage.

In an effort to more closely estimate the prevalence of infectious syphilis, we calculated the proportion of tests with high syphilis serologic titer (≥1:8), as persons with high titer are more likely to have infectious syphilis and less likely to be falsely reactive. 4 The denominator may include more than one test from the same individual if that individual was tested more than once in that setting. Data were submitted quarterly to CDC with the exception of Texas data, which were collected and submitted for only one to two quarters per year. Data were not available from South Carolina for delivery rooms in 1996 and for jails for the first half of 1996 and from Mississippi for 1999. Serologic (rapid plasma reagin [RPR]) testing was done at the individual state public health laboratories. The results of confirmatory treponemal testing were not available.

Prevalence data were analyzed by age group, sex, and site of testing. Where data from research centers were combined for analysis, data were adjusted by research center for each age group by the direct method of adjustment 5; prevalences of reactive serology for each research center were summed within each age group and divided by the number of research centers contributing data to the sum. Annual prevalence of high titer–reactive serology in jails was compared with annual county-specific primary and secondary syphilis case rates from 1995 to 1999. Primary and secondary syphilis case rates were derived from cases of primary and secondary syphilis reported to the CDC from state health departments for 1995 through 1999 and were calculated per 100,000 persons on the basis of population denominators from the Bureau of Census. 2 Linear regression analysis was performed to evaluate the relationship of case rate to prevalence of reactive serology. Data were analyzed with the SPSS statistical analysis package (SPSS, Chicago, IL).

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Results

Data on 106,326 serologic tests were submitted to CDC during the study period, including 36,904 from Louisiana, 7,120 from Mississippi, 13,866 from South Carolina, and 48,436 from Texas. Data on 105,130 tests were available for analysis, including 22,084 tests from delivery rooms, 3,088 from drug treatment centers, and 79,958 from jails (Table 1). In delivery rooms, 44% of tests were from women of Hispanic ethnicity (the majority of these tests were from Texas), 35% were from African American women, and 8% were from white women. In drug treatment centers, 57% of tests were for persons of African American race, 33% were for persons of white race, and 9% were for persons of Hispanic ethnicity. In jails, 64% of tests were for persons of African American race, 29% were for persons of white race, and 5% were for persons of Hispanic ethnicity.

TABLE 1

TABLE 1

The overall prevalence of reactive serology varied by site and was lowest among women in delivery rooms (2.9%) and highest among women in jails (11.1%) (Table 1). In jails and drug treatment centers, the prevalence of reactive serology among males was approximately half that among females. In all venues, prevalence was lowest in the youngest age group, and overall, reactive serology increased with age (Table 1).

The prevalence of high titer–reactive serology was one seventh that of the prevalence of all reactive serology in delivery rooms and one half to one third that in drug treatment centers and jails (Tables 1 and 2). The prevalence of high titer–reactive serology was similar to reactive serology in that it was lowest among women in delivery rooms (0.4%) and highest among women in jails (4.1%) (Table 2). Overall, high titer–reactive serology was half as prevalent among males in comparison with females and lowest in the youngest age groups. Prevalence of high titer–reactive serology tended to increase with age (Table 2).

TABLE 2

TABLE 2

In delivery rooms, the prevalence of high titer–reactive serology declined from 0.8 to 0.3 in Texas (1996–1999), from 0.4 to 0.3 in South Carolina (1997–1999), and from 0.6 to 0.0 in Louisiana (1996–1999). Among women in drug treatment centers, high titer–reactive serology declined from 4.9 to 4.8 in Texas (1996–1999), and from 2.4 to 0.0 in Louisiana (1996–1999), but did not decline in South Carolina. Among men in drug treatment centers, high titer–reactive serology declined from 2.8 to 1.0 in Texas (1996–1999), from 2.4 to 0.9 in South Carolina (1996–1998), and from 2.5 to 0.0 in Louisiana (1996–1999). Among women in jails, the prevalence of high titer–reactive serology declined from 9.5 to 2.4 in Texas (1996–1999), from 8.7 to 5.2 in South Carolina (1996–1999), and from 2.2 to 0.6 in Louisiana (1996–1999) but did not decline in Mississippi. Among men in jails, the prevalence of high titer–reactive serology declined from 2.1 to 0.9 in Texas (1996–1999), from 2.6 to 1.1 in South Carolina (1996–1999), from 4.9 to 3.0 in Mississippi (1996–1998) and from 1.2 to 0.4 in Louisiana (1996–1999).

The prevalence of high titer–reactive serology for males and females in jails was compared with county-specific P&S syphilis case rates by year for 1996 through 1999 (Figures 1–4). In Louisiana, Mississippi, and Texas, trends for prevalence of high titer–reactive serology and case rates were roughly parallel. Trends in South Carolina were similar until 1999, when the case rate increased and the prevalence declined slightly. The case rate and prevalence were compared by regression analysis. In Louisiana, 67% of the variance in case rates can be explained by the prevalence of high titer–reactive serology (R2 = 0.67;P = 0.17); in Mississippi, 58% of the variance in case rates can be explained by the prevalence of high titer–reactive serology (R2 = 0.58;P = 0.45); and in Texas, 51% of the variance in case rates can be explained by the prevalence of high titer–reactive serology (R2 = 0.51;P = 0.28). In South Carolina, only 20% of the variance in case rates can be explained by the prevalence of high titer–reactive serology (R2 = 0.20;P = 0.54). None of the correlation coefficients were statistically significant, most likely due to insufficient statistical power.

Fig. 1

Fig. 1

Fig. 2

Fig. 2

Fig. 3

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Fig. 4

Fig. 4

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Discussion

The prevalence of reactive serology in these counties was alarmingly high and far exceeded the 1976 to 1980 National Health and Nutrition Examination Study (NHANES) finding of 0.81% in the general population. 6 However, the prevalence in this study was similar to that found in NHANES among those with <$6000 annual income: 2.42% overall, with 1.45% among whites and 5.91% among African Americans. The twofold higher prevalence among women in drug treatment centers and jails is not surprising, as a greater proportion of women than men in drug treatment and jail are more likely to have participated in the exchange of sex for drugs, an activity which places them at high risk for syphilis. 7 These gender difference are consistent with the NHANES data for African Americans: there is a higher overall prevalence of reactive serology among women than among men (3.36% versus 2.68% [NHANES]).

There is a much lower prevalence of reactive serology among women in delivery than among those in drug treatment and jail. Parturient women as a group are probably at much lower risk for syphilis than women in jail and drug treatment. Noteworthy is the ratio of the prevalence of reactive serology to high titer–reactive serology: only 1 in 7 parturient women had a high titer, compared with 1 in 2.5 women in drug treatment and jail. These data indicate that in comparison with women in jail and drug treatment centers, parturient women have both lower prevalence and a lower proportion of high titers and are less likely to have infectious syphilis. Pregnancy and prenatal care may have provided some additional access to syphilis treatment.

The association of increasing prevalence of reactive serology and increasing age has been demonstrated in serologic surveys of syphilis 6 and is to be expected; as age increases so does cumulative exposure. However, it was unexpected to find that the prevalence of high titer–reactive serology also increased with age, indicating that older persons were more likely to have untreated or recently treated syphilis. This finding warrants further investigation.

These data demonstrate that trends in prevalence of high titer–reactive serology in jails may be a reasonable surrogate for trends in community case rates. Correlation between case rates and prevalence of high titer serology was high in three of the four sites. Lack of correlation between case rates and prevalence in the remaining site may have been influenced by the ability of the STD program to detect infectious cases. The ability of the STD program to ascertain cases may be affected by access to care, whether people at risk are appropriately tested, whether laboratories and providers report cases, and the existence and competency of field staff members to interview cases and elicit information about and follow up with partners.

Complete case reporting requires the success and synchronization of a number of program functions. Lack of correlation between prevalence monitoring data and case reports can be useful in alerting the program officials to deficiencies in program function, focal changes in morbidity, and healthcare system issues that need evaluation and attention. Syphilis seroprevalence monitoring is stable and independent of program function. It is a useful adjunct to case-reporting and simply requires public health agencies to evaluate trends in syphilis seroreactivity in populations regularly and systematically screened for syphilis.

This study had the following limitations. Data were not consistently available from South Carolina in 1996, and data from Texas were available for only 4 of 12 quarters during the study period. The lack of these data could affect the observed trends. The denominators in jails and drug treatment centers may include more than one test from the same individual if that individual was tested more than once in that setting. Data have not been evaluated for repeated tests, but it is thought that persons tested more than once comprise a small proportion of the population. Syphilis screening is not always consistent in jails. Although the research centers support universal testing in jails, there are some operational barriers, and a small fraction of persons are occasionally missed. Finally, the regression analysis was underpowered to detect a statistically significant correlation, as there were so few data points for comparison, and large variance. Stronger conclusions could have been drawn from this analysis had there been additional research centers for comparison or if syphilis serology and case rates had been tracked over a longer period of time.

Syphilis rates in the United States are at an historic low. Syphilis is increasingly manifested as a disease characterized by sporadic epidemics rather than a persistently endemic disease. 8 In October 1999, the Division of Sexually Transmitted Disease (STD) Prevention, of the National Center for HIV, STD, and TB Prevention, in collaboration with federal partners, state and local health departments, community-based organizations, and researchers, presented the National Plan for Elimination of Syphilis from the United States. 9 The five key strategies of the plan focus on enhanced community involvement and partnerships at local, state, and national levels, enhanced surveillance, expanded access to quality health care for those with or exposed to syphilis, improved health promotion, and rapid outbreak response.

Enhanced surveillance is a cornerstone of syphilis elimination activities. Surveillance efforts must include not only provider and laboratory reporting but also routine evaluation of syphilis test data. 9 The seroprevalence data from the ISP project demonstrate that trends in seroprevalence are similar to case-reporting trends. Syphilis seroprevalence data, especially those collected from large, stable numbers of persons in high-risk settings such as jails, can be used as an independent measure of syphilis trends and to augment syphilis case report data for syphilis program planning.

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References

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2. Division of STD Prevention. Sexually Transmitted Disease Surveillance, 1999. U.S. Department of Health and Human Services, Public Health Service. Atlanta: Centers for Disease Control and Prevention, November 2000.
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