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Condom Effectiveness: Factors That Influence Risk Reduction

FITCH, J. THOMAS MD*; STINE, CURTIS MD; HAGER, W. DAVID MD; MANN, JOSHUA MD, MPH; ADAM, MARY B. MD§; MCILHANEY, JOE MD

Article

This review summarizes those factors that limit the potential effectiveness of condoms in reducing the risk of non-HIV STI transmission.

From the *Department of Pediatrics, University of Texas Health Sciences Center at San Antonio, San Antonio, Texas; †The Medical Institute for Sexual Health, Austin, Texas; ‡Department of Obstetrics and Gynecology, University of Kentucky College of Medicine, Lexington, Kentucky; and §Department of Pediatrics/Department of Surgery, University of Arizona College of Medicine, Tucson, Arizona

Reprint requests: J. Thomas Fitch, MD, Department of Pediatrics, University of Texas Health Sciences Center at San Antonio, 7959 Broadway, Suite 604, San Antonio, TX 78209.

Received for publication December 5, 2001,

revised February 6, 2002, and accepted March 1, 2002.

ANECDOTAL REPORTS of devices used to sheath the penis during sexual intercourse date to ancient Egypt, but the earliest published description of the male condom was in 1564 by the Italian anatomist Gabriello Fallopio. Fallopio suggested that condom use could prevent contraction of syphilis. 1 Beginning in the 1930s, latex male condoms were promoted in the United States to prevent both pregnancy and sexually transmitted diseases (STDs), and condom use escalated during World War II. During the 1960s—coincident with the introduction of oral contraceptives in the United States—condom use declined, but that decline reversed following the discovery of HIV transmission routes and the search for an effective intervention to prevent HIV transmission. 2–4

Since 1985, results of numerous scientific studies delineating condom effectiveness in reducing HIV risk have been published. 5–7 However, episodes of debate about the effectiveness of condoms in reducing the transmission risk of other STDs—like the discussion triggered by a 1971 letter to the editor of The New England Journal of Medicine 8 —occur periodically. The most recent chapter in the debate about condom effectiveness has continued since a 1995 report showed that subjects who reported “always” using condoms were not at reduced risk of contracting one of several STDs. 9

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NIH Condom Effectiveness Conference

In June 2000 the four federal agencies responsible for condom research, condom regulation, condom use recommendations, and preventing new HIV and STD infections cosponsored “a workshop to evaluate the published evidence establishing the effectiveness of latex male condoms in preventing HIV/AIDS and other STDs.” A panel of 28 individuals—including representatives from the sponsoring agencies, STD/HIV researchers, clinicians, and other experts–was convened to “review and discuss the existing literature and write a report.”10

Using literature searches and other means to identify peer-reviewed publications, the panel members located 138 articles published in or before June 2000. Following their review of each article, panel members assessed the quality of the scientific evidence presented in each. Some studies reviewed were specifically designed to evaluate condom effectiveness, while others examined condom use as one of a number of independent variables predicting STD infection risk. The results of many published studies were compromised by weak study design, while other investigations–including studies of serodiscordant HIV couples–were determined to have strong designs.

Upon review, evaluation, and discussion of the submitted articles, panel members agreed that “The published data documenting effectiveness of the male condom were strongest for HIV.” On the basis of results of a published meta-analysis, “‘always’ users of the male condom significantly reduced the risk of HIV infection in men and women…who engage in vaginal intercourse.” Panel members also agreed that on the basis of consistent findings in four epidemiologic studies, “the latex male condom could reduce the risk of gonorrhea for men,” and “might afford some protection in reducing the risk of HPV-associated diseases, including warts in men and cervical neoplasia in women.”10

While acknowledging the possibility that condoms reduce the risk of HPV-associated diseases, the panel members also concluded that “there was no epidemiologic evidence that condom use reduced the risk of HPV infection.” Further, the panel concluded that the existing data provide insufficient evidence to conclude that condoms reduce one's risk of contracting or transmitting the following STDs: chlamydial infection, syphilis, chancroid, trichomoniasis, and genital herpes. There were also insufficient data to confirm condom effectiveness for reducing the risk of gonorrheal infection in females and HPV infection in men. The panel further acknowledged that condoms do not eliminate the risk of any STD, but it stressed “the absence of definitive conclusions reflected inadequacies of the evidence available and should not be interpreted as proof of the adequacy or inadequacy of the condom to reduce the risk of STDs.”10

While the panel acknowledged that the absence of definitive studies does not necessarily indicate the inadequacy of the condom, a logical question remains: Why did the published literature show that consistent condom use reduced the risk of HIV transmission and gonorrhea acquisition by males but not the risk for other STDs? A similar question concerns why studies show risk reduction for gonorrhea in males but are inconclusive for females.

Future studies that use better research methods may eventually document risk reduction for other non-HIV STDs. Another plausible explanation for the lack of scientific evidence of condom effectiveness is that other factors—factors other than condom use alone—affect the transmission of many non-HIV STDs. This review includes a discussion of those “other factors” that influence condom effectiveness.

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Definitions

Efficacy is the improvement that can be achieved in a desired health outcome with use of an intervention in a research setting by expert subjects under ideal conditions. 11

Effectiveness is the improvement that can be achieved in a desired outcome with use of an intervention in a target community (or by an individual in the “real world”) under resource constraints and with typical use. 11

Method failure is the failure of a protective device that is dependent on the physical properties of the device. Note: with regard to the latex condom, combined slippage and breakage rates are commonly referred to as method failures. Another form of method failure occurs when a condom is used consistently and correctly but infection is transmitted by direct contact with infected skin or skin lesions that lie outside the areas covered by a male condom (vulva, scrotum, thighs, etc.).

User failure is the failure of the device due to incorrect and/or inconsistent use. Note: slippage during intercourse is usually considered a method failure, but slippage during withdrawal is considered a user failure.

Perfect use is obtained by using a condom for every act of intercourse and following the recommended steps for correct condom use during each use. Note: only one of the studies reviewed mentioned both “correct” condom use and condom use during every act of intercourse. 12

Always use is using a condom during every act of intercourse.

Never use is not using a condom during any act of intercourse.

Typical use is using a condom more often than never use but less often than always use. Typical use includes consistent and inconsistent use, as well as correct and incorrect use.

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Other Issues Requiring Clarification

Risk Reduction Versus Prevention

The language used to describe the potential benefits of condom use can be confusing. Feldblum and Cates make the following statement: “Product labeling and counseling of people at risk have to make a clear distinction between absolute protection (‘prevents infection’) and partial protection (‘reduces the risk of infection’).”13

Given the ever-present risk of infection due to method failure alone, one should not expect condom use to prevent infection. Risk reduction may be a legitimate expectation, but the amount of risk reduction is influenced not only by user failure (inconsistent and incorrect use) and the mode of disease transmission, but also by other disease-specific factors such as the “disease-specific infectivity,” or DSI.

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Cumulative Risk

Cumulative risk is the likelihood of an outcome occurring at least once, given a repeated number of risk exposures. Feldblum and Cates say this about cumulative risk: “Another important counseling point is that single-episode (condom) efficacy and the cumulative (condom) efficacy diverge widely as the number of exposures to an infected person increases.”13 For example, an intervention that is 99.8% effective for a single episode of intercourse can yield an 18% cumulative failure rate with 100 exposures.

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Factors That Influence Condom Effectiveness

The following list contains additional factors that influence whether a condom will effectively reduce the risk of transmission (or acquisition) of an STD.

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Mechanical Qualities of Condom Materials

An intact latex barrier should contain the infectious agents for all known STDs that are transmitted by the exchange of infected bodily fluids. 14–16 Some studies show leakage of virus-sized particles through intact latex barriers, but actual infection from such leakage is unlikely, and this leakage is probably not a significant factor in disease transmission. 17–19

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Mode of STD Transmission

For STDs spread by genital fluids (HIV, gonorrhea, chlamydia, and trichomoniasis), an intact latex condom should prevent one's risk of infection following a single sexual exposure–provided the condom is used according to the seven 7 steps for correct use recommended by the CDC and does not slip or break. For STDs classified as genital ulcer diseases (genital herpes, syphilis, and chancroid) and for HPV (which appears to be transmitted both by direct contact and through genital fluids), an intact latex condom may not reduce one's risk for a single act of sex, even when the condom is used “correctly” and does not break or slip. Despite even correct condom use, significant risk of infection may remain because disease transmission can occur from infected skin or lesions not covered by the condom.

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Method Failure (Slippage and Breakage)

Even when a condom is used consistently and correctly, slippage and breakage can occur. Studies demonstrate that slippage or breakage occurs between 1.0% and 3.6% of the time. 20–22 The reported slippage and breakage rates are even higher for less experienced users. 23,24

A large French national survey reported differences in slippage and breakage rates between couples with less than 5 years of condom experience and couples with more than 5 years of experience. Couples with greater than five years of condom experience reported 0.8% breakage and 0.7% slippage, for a total method failure of 1.5%. Those with less than five years of condom experience reported a 6.2% breakage rate and a 1.8% slippage rate, for a total method failure of 8.0%. 23

Condom breakage and slippage can also result in pregnancy. In a large study of over 17,000 women, a difference in condom failure rates was determined to depend on the number of years of condom experience. Among married women aged 25 to 34 years, the pregnancy rate for those with less than 2 years of condom experience was 6.0%. When the length of condom experience increased to 25 to 48 months, the pregnancy rate declined to 4.0%, and with 49 months of condom use, the pregnancy rate was 3.6%. 25

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User Failure

The form of user failure that carries the greatest risk of infection is clearly condom nonuse. If condoms reduce the risk of contracting/transmitting any STDs, that benefit is lost or substantially diminished when condoms are not used for each and every act of intercourse. In addition to inconsistent use, condom effectiveness is also compromised by incorrect use. Incorrect use means not performing all the recommended 7 steps for correct use before each act of intercourse. 26

Incorrect use can take many forms, for example, initiating genital contact before putting on a condom or using a condom with a petroleum-based lubricant. Another potential form of incorrect use is the practice of “reversing” or flipping the condom over after having first placed it on the penis with the wrong side down. Improper initial positioning of the condom makes unrolling the condom difficult. When initial attempts to unroll the condom fail and the condom is flipped over, any secretions—including sperm-containing pre-ejaculate and/or infectious fluids–that remain on the condom may be in direct contact with the vagina and cervix during vaginal intercourse. 27

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STD Infectivity

Infectivity means “infectiousness” and is a measure of one's risk of infection given an exposure to an infectious disease. Infectivity is sometimes expressed as a “per-partnership infectivity” and at other times as “per-act infectivity.” Different sexually transmitted infections have different infectivities. The reported STD infectivities range from 0.001 for HIV 28,29 to 0.70 for chancroid. 30 (Note: the infectivity of HIV varies with the stage of the disease, treatment status, and other variables.)

Infectivity varies not only by disease but also, for a given disease, often by gender. For example, with gonorrhea, males have a 0.20 infection risk per act of sexual intercourse with an infected partner, but females have at least a 0.50 risk of infection per act with an infected partner. 31–33 Condom failure is more likely to result in infection when that failure exposes one to a particularly infective STD. 34

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Presence of Other STDs

The presence of another STD—particularly, an ulcerative disease–can significantly increase the risk of acquiring (or transmitting) HIV. 35 It is unknown whether the presence of a non-HIV STD can increase the risk of acquiring (or transmitting) another non-HIV infection.

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Age and Sex

The columnar cells covering large exposed portions of the young adolescent cervix are more susceptible to certain infectious agents—including HPV, Neisseria gonorrhoeae, and Chlamydia trachomatis—than are the squamous epithelial cells that typically cover most of the adult cervix. When adolescent females with this cervical condition (“cervical ectopy”) come in contact with these infectious agents, infection is more likely. 35

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Number of Exposures

Peterman points out that the total number of sex acts (exposures) is an important variable in determining condom effectiveness. 36 This concept is supported by the mathematical modeling work of Mann et al 34 and is discussed further in the following section on Cumulative Risk.

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Cumulative Risk

The issue of cumulative risk was not addressed in the NIH panel's report. Cumulative risk is the likelihood of an outcome occurring at least once, given a repeated number of risk exposures. How effectively a condom can reduce one's infection risk for a single act of sex with an infected partner is important, but what happens to the risk of infection after repeated exposures—even for “always” condom users—helps determine whether the uninfected partner ultimately becomes infected.

Mann et al, 34 for example, show that if one assumes a 3% slippage and breakage rate and a disease-specific infectivity of 0.50, then the expected risk reduction for one act of sex with an infected partner while using a condom correctly is 98.5%. The calculated cumulative risk of condom failure is 14% for 10 acts of sex with an infected individual, 26% for 20 acts of sex, and 37% for 30 acts.

If incorrect condom use is added to the likelihood of condom breakage and slippage, the risk of exposure and subsequent infection is also higher. According to Warner et al, 27 in a population of self-selected well-educated men who averaged more than 5 years of condom experience, 10% of all condom uses left the male user with a potential risk of infection (slippage, breakage, and incorrect use). The authors concluded: “Given the level of exposure to unprotected intercourse during condom use in this population, we suspect that exposure levels may be even greater in less-experienced, less-educated populations, such as new condom users and adolescents.”27

If the findings of Warner et al 27 of a 10% disease exposure rate is correct, 40% of consistent condom users would experience infection after just 10 sex acts if the disease in question has an infectivity of 0.50. Thirty acts would result in 79% being infected, even for consistent condom users. The risk of infection would be substantially higher if less than consistent condom use occurs.

There was no discussion among panel members about the phenomenon of “partial herd immunity.” Typically, this phenomenon has been recognized to benefit populations when even a partially effective prevention intervention is widely implemented in high-risk groups. 37 If condoms are eventually proven to reduce the risk of STD transmission and if consistent and correct use is broadly implemented, such a population effect may be seen. To date, however, condom effectiveness for most STDs has not been demonstrated and broad-scale consistent and correct condom use has not been achieved.

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Studies That Measure Condom Effectiveness: Risk Reduction for Multiple STDs

The NIH Condom Effectiveness Panel examined the degree of risk reduction afforded by condom use for each of eight common STDs. The results from the three cohort studies that measured aggregate outcomes for multiple infections were generally excluded. An exception was the inclusion of selected data about chlamydia from the Zenilman study. 9 We feel that the findings of these studies should be discussed here.

The cohort study reported by Zenilman et al 9 was a prospective investigation conducted in Baltimore STD clinics. Extensive sexual histories were obtained from all study subjects, who additionally were evaluated for the presence of an STD. When identified at the intake examination, existing nonviral STDs were treated. Subjects were then followed for the development of four incident STDs (gonorrhea, chlamydia, syphilis, or trichomoniasis). Those who were infected at the 3-month visit were classified as having a new infection.

Of those with new infections, 15% of the men who “always” used condoms were newly infected, compared with 15.3% of “never users.” Twenty-three and one half percent of women who reported that their male partners “always” used condoms had a new STD, compared with 26.8% of women who said their partners “never” used condoms. These differences in the development of new infections between the “always” and “never” condom users were not statistically significant.

The authors gave three explanations why their study failed to demonstrate a significant relationship between self-reported condom use and new STDs, but none of these explanations mentioned the possibility of condom failure (breakage or slippage) or the cumulative risk of infection as an explanation. Nor were these issues mentioned in the many letters to the editor that followed publication of the article.

Another prospective study with multiple measured outcomes 38 is a model for future STD research. This was a prospective 6-month cohort study conducted in four teen clinics. Eligible subjects included sexually experienced females aged 14 to 19 years being seen for a visit that included a pelvic examination. Patients were excluded who (1) were being seen for a refill of oral contraceptives, (2) were being seen for a follow-up visit following the diagnosis of an STD, or (3) had taken antibiotics within the previous 2 weeks. The study was conducted under a grant from the CDC and was supervised by CDC personnel.

Only 12% of the visits were to confirm symptoms suggestive of infection. Despite this, 40% of the subjects were infected with an STD at the enrollment visit and many had multiple STDs. Eighty-seven percent of the girls with any STD were asymptomatic.

Females with nonviral infections identified at the initial visit were treated and, where appropriate, tested for cure. CDC-trained personnel counseled subjects about condom use and encouraged subjects to have their partners seek treatment. At the 6-month follow-up, 23% of the participants had a new infection. Self-report by subjects of consistent (“always”) condom use did not significantly reduce their risk of having a new STD. Furthermore, only 12.6% of the participants had maintained “always” condom use.

The authors stated: “While it would be inappropriate to generalize findings from this study to the entire adolescent population, this teen clinic population is likely to be more representative of sexually active female adolescents than STD clinic populations who are more commonly studied, since the majority of teens who presented at the teen clinic were asymptomatic.”

In attempting to explain the study results, the authors cited three potential explanations for the lack of significant impact: (1) incorrect condom use, (2) biased self-reporting, or (3) women who reported condom use might have been more likely to select high-risk partners. Again, no mention of the cumulative risk of condom failure was offered to explain these.

The weakest of the three cohort studies was a 1999 study that measured subsequent STDs among adolescent women with genital infection: chlamydia, gonorrheal, or Trichomonas vaginalis. 39 The study design combined differing patterns of self-reported condom use (“most of the time” and “all of the time” use) into a single category. “Never” use and “rarely” use were also combined into a category called “never/rarely” use. These hybrid categories were compared, but the comparison failed to demonstrate statistical significance in the findings. Additionally, 52% of participants were lost to follow-up.

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Discussion

Condoms are widely believed to be highly effective in preventing HIV and non-HIV STDs if they are used consistently and correctly. Labels on condom packaging regularly indicate that condoms are effective in preventing multiple STDs. Educational materials from many professional and governmental organizations acknowledge that condoms are not 100% effective but fail to discuss the actual or predicted effectiveness or additional factors that may influence condom effectiveness. The origin of these assumptions of condom effectiveness in preventing STD transmission is uncertain, but they may be the result of extrapolation from studies that measured the effectiveness of condoms for preventing the transmission of HIV or from laboratory studies about the physical qualities of latex.

As stated previously, the members of the panel from the NIH Condom Effectiveness Workshop found that “always” use of condoms could reduce the risk of acquiring HIV infection for both men and women and reduce the risk of acquiring gonorrheal infection for males, but that the data were inconclusive for other STDs, including genital herpes. A study published since the development of the NIH Condom Effectiveness Workshop Report demonstrated risk reduction for genital herpes with “inconsistent” condom use for women, but not for men. This methodologically excellent study was limited by the small number of newly infected individuals from whom condom use histories could be obtained. In addition, it demonstrated the challenges of changing behavior, as only 13% of serodiscordant couples reported that they “always” used condoms. 40

Three longitudinal cohort studies that measured associations between self-reported condom use and the presence of multiple STDs showed no reduction of STD risk, even for “always” condom users. 9,38,39

While the factors that affect STD transmission—infectivity, consistency of condom use, correctness of condom use, and the percentage of slippage and breakage—are important, disease-specific infectivity and consistency of use appear to be most important when slippage and breakage are factored in. Mathematical models predict that with increasing numbers of exposures to an infected partner, one's risk of infection—even with perfect condom use—increases, particularly with exposure to highly infectious STDs. Imperfect or inconsistent condom use would be expected to cause further dramatic risk increases. 34

The presence of an existing STD infection probably increases the transmissibility of and/or susceptibility to HIV infection. In this situation, condom effectiveness in preventing the transmission of HIV infection is likely to be diminished.

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Public Health Implications

Many of the published, peer-reviewed articles reviewed by the NIH Condom Effectiveness Workshop Panel that form the basis for this information have been available for some time. Nonetheless, many of the issues and concerns identified by the panel are “new” to both the public and to clinicians who counsel patients in their practices. Efforts to communicate this “new” and vital information—the proven benefits, known risks, and unanswered questions—to the public and to health professionals must now begin.

On the basis of this information, the authors suggest the following:

  1. In the absence of compelling evidence of condom effectiveness, young people should be strongly encouraged and counseled to delay the initiation of sexual activity. Studies have shown that delaying the onset of sexual activity markedly decreases the average number of lifetime sexual partners. 35,41,42 The number of lifetime sexual partners greatly influences the risk of STD acquisition. Delaying sexual initiation is particularly important because of the high incidence and prevalence of STDs in the adolescent population. Though this delay in sexual initiation will benefit both sexes, females are likely to receive the most significant health benefits. Allowing time for the epithelial cells of the female cervix to mature before any potential STD exposure occurs should provide measurable protection.
  2. Patients using condoms should be provided with information to explain the difference between absolute protection (which prevents infection) and partial protection (which reduces the risk of infection). Condom users must know that condoms, at best, reduce their risk of some STDs and may or may not reduce the risk of other STDs.
  3. Patients using condoms should be provided with the information that their risk of contracting an STD increases with the number of disease exposures—even when condoms are used consistently and correctly. This increase is even more dramatic with inconsistent or no condom use.
  4. Patients using condoms should be provided with the information that condoms are not equally protective for every STD. The actual degree of risk reduction provided by the condom depends on other factors, many of which are outside the user's control, including gender, mode of disease transmission, and disease-specific infectivity. Condoms appear to be “more forgiving” for STDs with low infectivities (such as HIV) than for STDs with high infectivities (such as gonorrhea in females).
  5. Patients using condoms should be provided with information about avoiding high-risk sex partners. Having sex with a prostitute or IV drug user is clearly a high-risk activity. Similarly, having sex with an individual who has (or has had) multiple sex partners is also a high-risk activity.
  6. All patients should be provided with the information that STDs often are asymptomatic and go unrecognized, even by those infected. Patients should understand the necessity of appropriate screening, even for consistent condom users.
  7. All patients identified as having an STD should be counseled that reinfection is common after STD treatment. To lower reinfection rates, one's partner must also be tested and treated. In addition, posttreatment testing to confirm cure may be indicated for certain STDs.
  8. Healthcare providers should actively identify patients in their practices who are engaged in risky behaviors, who have partners who admit to engaging in risk behaviors, or who, because of other characteristics, are members of a risk group. Once these individuals are identified, healthcare providers should systematically test them for STDs. Even patients who report “always” condom use should receive screening and/or testing. This requires healthcare providers to implement systems for collecting information about the sexual activity and risk status of each patient at every office visit and for counseling against involvement in risky sexual behaviors.
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