While press coverage of the July 22 government report on condom research has stirred debate in health policy circles, millions of Americans are left to wonder how much protection condoms really provide against sexually transmitted diseases (STDs).

Condoms have long been promoted both by public agencies and academic experts as the best form of STD prevention, and the purpose of the government report was to examine the scientific evidence on condom effectiveness. If we recommend condoms to sexually active people in order to reduce the risk of getting an STD, some wondered, did we have the research to back it up?

The answer contained in the government report (Scientific Evidence on Condom Effectiveness for Sexually Transmitted Disease Prevention) was a partial yes. The role of condoms in preventing the spread of HIV/AIDS is very well supported by recent scientific studies, the report says. And similar findings have been made in studies that measure condom effectiveness in preventing gonorrhea. Much weaker evidence shows a trend to reduce the risk of genital warts and cervical cancer caused by genital HPV infection, (human papillomavirus).

At the same time, however, the report noted that for several other widespread STDs, notably genital herpes, chlamydia, and trichomoniasis, there were few well-designed studies and no conclusions could be drawn because of the poor quality of the evidence (See Part 1 of this series, "Government Condom Report: What Does It Say?")

The evidence for condoms has always been partly circumstantial, experts say, and this has been common knowledge for decades. Laboratory tests have shown that latex condoms contain even the smallest sexually transmitted microbes. Studies also have documented lower rates of some STDs in people using condoms. However, scientists have had trouble designing condom studies with exactly the same scientific rigor that they apply to experimental drug studies, for example.

Ethics and Condom Research

By today's standards, the best studies are those that use a control group. In the context of condoms and STDs, this would mean a segment of study participants would be required not to use condoms, while subjects in the "experimental" group would use condoms. The two sets of study participants would then be followed over time, with differential rates of STDs noted in the final analysis.

But the catch here is that the study group not using condoms would be exposed to a greater degree of risk for acquiring HIV and perhaps other STDs. This has long been considered unethical, and the government report concurs. "Because condom research has been shown to reduce the risk of some STDs," it says, "research participants cannot be ethically randomized to use and non-use groups."

Willard Cates, Jr., MD, MPH, who directed the U.S. Centers for Disease Control's Division of HIV/STD Prevention from 1982 through 1991, says the "language of the report itself illustrates how the clinical and scientific community sets condom use to prevent sexually transmitted infections as a standard of care."

The major alternative to randomized trials are the so-called observational studies. For some of these, study subjects report on past sexual contacts and behaviors after the fact. This information is then combined with medical evaluations in calculating whether condoms did or did not have a protective effect. Some observational studies, however, are able to track subjects in the present rather than looking to the past; such prospective studies are considered superior. For these, researchers often recruit couples in which one partner has been diagnosed with a particular infection and the other is initially free of infection. Some of the studies the government panel accepted as proof of condoms' 85% effectiveness in preventing HIV were precisely this type of "discordant couple" study.

In general, observational studies can be used for viral STDs, such as HIV or herpes, because these are chronic infections. But for a bacterial STD, such as chlamydia, ethics would dictate using the existing treatment to eliminate the infection rather than waiting to see if it's transmitted.

The Latest Findings

Most public health officials agree that the government report was generally an adequate reflection of current science on condoms and STDs. But a number of scientists in the STD field point to important new evidence that was not considered as part of the government review because it had not yet been published.

The paper in question examines condom use in the prevention of genital herpes, one of the most widespread STDs, with up to 45 million Americans infected. CDC and other health agencies have long placed caveats on the notion that condoms protect against genital herpes, because condoms may not cover or protect all of the genital sites where herpes might be active. And the government panel reflected this uncertainty.

A recent paper in the Journal of the American Medical Association, however, showed that even inconsistent condom use significantly protected women in a study of genital herpes in discordant couples. The JAMA paper (June 27, 2001), authored by Anna Wald, MD, MPH, of the University of Washington, showed that women who used condoms during at least 25% of their sexual encounters had just 8% of the type 2 genital herpes risk found among women who used condoms less often.

Asked if the government report fairly assesses the role condoms in preventing genital herpes, Wald said the evidence now warrants "more than a medium-strength" recommendation. "It's a strong finding we had in our study," Wald says. "We haven't yet analyzed and published the data for men, but there's no reason to think that condoms don't work for men. I would endorse condoms for herpes prevention across the board."

What's next?

In the end, of course, millions of non-scientists are eager for simple advice on protection, and 'one-stop shopping' for all the STDs would be ideal.

"After reviewing 138 articles," says Cates, "the panel came to the conclusion that condoms protected against the most deadly STD-HIV-and the most easily transmitted STD-gonorrhea. In my mind, therefore, it's case closed: condoms do work and they should be promoted. Any other public health message is a misrepresentation."

But Cates and others interviewed for this piece also caution that condoms have never been presumed to give 100% protection, and they probably work better for some STDs than others.

Penny Hitchcock, former head of the STD Branch at the National Institute of Allergy and Infectious Diseases, says the public health would be well served by more research. Hitchcock, who co-chaired the workshop that preceded the government panel's final report, emphasizes that one STD might be quite different from another, even though all are spread through intimate contact.

"Some may be hard to catch and others may be easy, to catch" says Hitchcock. "The easier they are to transmit, the less forgiving they are about a condom 'mistake,' like forgetting to use it once or breaking it during use."

More studies to pinpoint the exact degree of risk reduction provided by condoms are recommended by the report, and Hitchcock sees these as a logical step. "Let's say the issue, instead of condoms, was a vaccine that prevented HIV and maybe other STDs," she notes. "The outcry for more studies would be deafening."

As the research community gears up for this work, many public health experts stress that the overwhelming evidence for condoms in HIV prevention is reason enough to use them, and they point out that the case for several other STDs is growing stronger. The consensus seems to be that the condom remains the good but less-than-perfect method it has always been.