In July 2001, the National Institute of Allergy and Infectious Diseases released a report of an invited workshop summarizing the empirical evidence on the effectiveness of condoms for the prevention of sexually transmitted diseases. 1 The report opined that condom use was effective for the prevention of HIV transmission, and for gonorrhea in men, but there was little extant data that could conclusively demonstrate effectiveness for other nonviral or viral infections, the common STD pathogens commonly seen by the millions annually in our nation’s STD clinics. A number of methodological problems have been identified in the Workshop Summary 1 and by other groups 2–5 assessing condom effectiveness for STD prevention. These include:1 how to determine consistency of condom use;2 how to properly measure correct condom use;3 determination of sexual partner infection status;4 how to account for social desirability bias, specifically, and the validity of self-reported risk behavior, generally;5 accounting for the social contexts in which infrequent condom users might be stimulated to use condoms, and 6 accounting for the varying sensitivity and specificity of different STD diagnostic assays that have been used over the past several decades.
The most consistent finding reported on condom use effectiveness has been data captured from HIV discordant couples in cohort studies. 6–8 In these studies, many of the measurement problems that have been identified are overcome by a prospective ascertainment of condom use, 9 reports on the consistency of risk behavior by both partners, 10 and knowing the infection status and risk behaviors of each partner. 11 Outside of HIV partner studies, there have been relatively few partner studies that have had the methodological rigor seen in the HIV discordant couple investigations. Either the number of couples has been limited, 12 the duration of follow-up limited, 13 or the number of incident STDs observed has been insufficient to draw inferences concerning condom use effectiveness with confidence. Most of the published literature on condom effectiveness for STD prevention comes from cross-sectional studies in which prevalent infection is associated with sexual practices determined retrospectively. 14–16 These designs are inherently weak and fraught with methodological problems. Of the few longitudinal cohorts (generally part of randomized behavioral intervention trials), the duration of follow-up has been relatively short and insufficient STD outcomes have been generally observed. 17–19
Nevertheless, in this issue of Sexually Transmitted Diseases, Shlay et al. 20 offer data that suggest that consistent condom use is effective for the prevention of a variety of viral and nonviral STDs. In their study of over 75,000 patients seen over a 12 year period at one urban STD clinic, condom use was reported by 54% of sexually active patients presenting to the clinic with a new problem. Of these patients, fewer than one-third of condom users (16% overall) gave a history of consistent condom use in the prior four months. Prevalence rates were calculated for gonorrhea, chlamydia, trichomonas, genital herpes, and genital warts that were first onset and symptomatic for only for the prior month, trichomonas and molluscum contagiosum, and presented by frequency of condom use in the prior 4 months. Overall, condom use showed only modest protection against the commonly seen STDs for both men and women. However, when the data were analyzed for condom users, comparing consistent versus inconsistent users, strong and relatively consistent findings emerged. For both men and women, prevalent gonorrhea and chlamydia were significantly reduced among consistent condom users, whereas genital herpes was lower for men, and trichomonas was lower for women, who reported consistent condom use.
The study by Shlay et al. 20 has a number of strengths. First, the sample size is very large. Many of the reported cross-sectional studies are relatively small, and lack sufficient statistical power to demonstrate associations for relatively rare outcomes, and most are definitely underpowered to demonstrate the effectiveness of condoms for the prevention of specific STDs. Importantly for study design and subsequent interpretation, the assays used for the detection of each STD in this study were systematically applied over the entire period of the study. Thus, there were no shifts in the use of assays with varying sensitivity and specificity over time. Given the large sample size, the authors were able to restrict their analysis to periods when reliable tests were available (for example, detection of C. trachomatis by nucleic acid amplification was limited to the period 1996-2001). The strategy of conducting a subset analysis, comparing consistent condom users to inconsistent users, demonstrated that the riskiest group were also those most likely to perceive this risk and use condoms consistently. This approach overcomes the bias inherent in analyzing ever versus never condom use, as the former category is a far from homogeneous group.
Although one might question the generalizability of the data, given that they are limited to residents of one city attending a single urban STD clinic, the large number of patients from a triethnic community is a methodological strength when analyzing racial/ethnic differences in behaviors, risks, and the effectiveness of condoms in preventing STDs. Perhaps of greatest importance is the consistency of the effectiveness of self-reported condom use for the reduced prevalence of each specific STD analyzed for both men and women. These findings lend credibility to the assertion in STD prevention counseling that condoms are be an important strategy for reducing risks associated with acquiring STDs. Our evidence base to support our practice in the clinical STD encounter is now buttressed by these data.
Cross-sectional data have a number of inherent limitations, which apply to the Shlay et al. study. 20 The authors conclude their investigation with a litany of shortcomings of their study design and methods, most of which they suggest actually underestimate the protective effectiveness of condoms, including the retrospective ascertainment of a very limited repertoire of sexual behaviors and no information about the infection status of sexual partners. However, in a busy clinic setting where research is conducted ancillary to the provision of clinical care, these limitations are understandable, if not regrettable. To overcome them requires an enormous reallocation of resources (both financial and personnel) that would be an unlikely priority in a local governmentally funded setting. One remaining measurement issue that has been widely acknowledged is that of measuring condom use technique, or ‘correctness’ of use. 18 There is no agreed upon standard for measuring correctness of condom use, and condom demonstration on dildos may not reflect how condoms are used in reality.
Was the Workshop Summary 1 of the NIH 2001 meeting harmful to the field of STD prevention? Certainly, advocates of condoms for the prevention of STDs might have taken umbrage at the conclusions reached. However, hard-nosed realists would have to conclude that the quality of the data in the published literature was dubious and replete with methodological shortcomings. The evidence base on the field use effectiveness of condoms may now be somewhat shored up with the publication by Shlay et al. 1 Additional studies are clearly warranted, particularly those that use highly sensitive STD assays, within the context of either prospective studies or in randomized controlled trials.
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