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Sexual Network Data Help Assess Putative STD Reporting Bias


Letter to the Editor

From the STD/HIV Programs, El Paso County Department of Health and Environment, Colorado Springs, CO; and the Department of Preventive & Community Medicine, Emory University School of Medicine, Atlanta, GA.

Address for correspondence: John J. Potterat, BA, STD/HIV Programs, El Paso County Department of Health and Environment, Colorado Springs, CO.

To the Editor:

In their comprehensive review of surveys used to assess community sexually transmitted diseases (STD) patterns, Ku and colleagues advocate obtaining integrated behavioral and clinical data.1 In particular, they recommend seeking information about the sexual partners of STD patients “(e.g., partner gender, age, race, where and how this partner was met, whether the partner was a prostitute or drug user, perception of partner's promiscuity). These could help us understand more about the sexual networks that promote transmission of STDs.”1 This is sound advice. Indeed, such data might have prevented Zenilman, in his accompanying editorial,2 from suggesting that a certain ascertainment bias may be responsible for observed disparities in case reporting by sex and ethnicity. Although not specified in the following quote, its context suggests that Zenilman is referring to gonorrhea: “Private sector underreporting has been well documented and probably underlies the disparate male-female ratio seen in whites.” In the United States, the male-female ratio in reported gonorrhea cases among non-Hispanic whites is virtually the inverse of that reported in non-Hispanic blacks for the period 1992 to 1995 (0.6:1 compared with 1.3:1, respectively).3 Where, then, are the “unreported” white men? Zenilman suspects the following bias: “It is well recognized that in the STD context, race may be a surrogate for socioeconomic status and/or health care access and that this rate [sic] differential may be overrepresented in the national surveillance data.”2 We suspect he means that whites are likelier to have access to private providers whose reporting practices may be influenced by their patients' demographic profile.

The male-female ratio is a time-honored measure in STD control. A deviation from 1.0 is often explained by invoking homosexual activity (usually men having sex with other men, accounting for a large number of men compared with women) or by biases in reporting or case finding systems (screening/contact tracing). Interpretation of the sex ratio (by race, in this case) is actually more difficult. Decomposed, it is the summation, over individuals, of the number of infected contacts per infected case and the race mixture of those contacts. The latter, in turn, is the result of the infected person's mixing pattern (i.e., the sexual network). The end result-the sex ratio by race-does not contain any of this information and thus permits little more than speculation.

Our community-wide gonorrhea data,4 obtained in periods of intensified surveillance and saturation contact tracing, indicate that our observed race-sex case distribution is less likely to reflect such artifacts than to truly mirror the local epidemiology of gonorrhea: white women with gonorrhea frequently report sexual exposure with non-white men,5 and black men with gonorrhea frequently report sexual exposure with non-black women.6 It is suggested by the national data that this local phenomenon may admit of some generalizability: If one merges white and black gonorrhea case reports by sex, many of the white men (and black women) “missing” from case reports could be accounted for. In addition, the resulting male-female ratio (1.2:1) would be the same as that for overall gonorrhea case reports (1.2:1) and would approach that for Hispanics and other ethnic groups (1:1).3 Moreover, if sex disparity by ethnicity in gonorrhea case reports truly sprang from the Zenilman-suspected bias, how do we explain the virtual parity in male-female ratio for the same two ethnic groups (non-Hispanic blacks and whites) in reported cases of primary and secondary syphilis during the same period?3 That syphilis, being a more “serious” infection, is likelier to be uniformly (i.e., white men included) reported by a provider?

Providing empiric evidence from partner mixing patterns that the disparity in gonorrhea case reports by sex or ethnicity probably reflects real epidemiologic events reinforces the appeal of Ku and colleagues that sexual networks data be part of routinely collected STD survey information. In particular, we recommend obtaining data that can show the distribution of STD patients' partner mixing patterns, rather than data about the frequency of one group's mixing with another. In other words, network information is critical for assessing the ratio of men and women involved in transmission as well as in reports. Without such data, there is little basis on which the assume bias purely because the ratio of reported males to females is not 1.0.

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1. Ku L, Sonenstein FL, Turner CF, Aral SO, Black CM. The promise of integrated representative surveys about sexually transmitted diseases and behavior. Sex Transm Dis 1997; 24:299-309.
2. Zenilman JM. New paradigms for sexually transmitted diseases surveillance and field studies. Sex Transm Dis 1997; 24:310-311.
3. Division of STD Prevention. Sexually Transmitted Disease Surveillance, 1995. U.S. Department of Health and Human Services, Public Health Service. Atlanta: Centers for Disease Control and Prevention, September 1996.
4. Potterat JJ, Rothenberg RB, Woodhouse DE, Muth JB, Pratts CI, Fogle JS. Gonorrhea as a social disease. Sex Transm Dis 1985; 12:25-32.
5. Potterat JJ, Woodhouse DE, Pratts CI, Markewich GS, Fogle JS. Women contacts of men with gonorrhea: case-finding yields. Sex Transm Dis 1983; 10:29-32.
6. Rothenberg RB, Potterat JJ. Temporal and social aspects of gonorrhea transmission: the force of infectivity. Sex Transm Dis 1988; 15:88-92.
© Copyright 1997 American Sexually Transmitted Diseases Association