A Staff Report from the Straight Dope Science Advisory Board

Do condoms protect against STDs other than HIV? STD-wise, how risky is oral sex?

September 18, 2007

Do latex condoms provide adequate protection against all STDs? I know they are effective against HIV, but are they effective against HPV or herpes? Also, how dangerous is it for a man to receive oral sex from a woman without a condom?

Good questions, Josh. Let's start off with a basic premise, as laid out last year in the New England Journal of Medicine: "[T]he protection that condoms offer against a specific sexually transmitted infection cannot be precisely quantified." The article gives a few reasons. First – well, it's a bit awkward to discuss, really, but researchers studying condom use don't typically watch their subjects use condoms to make sure that (a) they really are using them, and (b) they're using them correctly; instead, they rely on self-reporting, the reliability of which is suspect. Second, the transmissibility of HIV specifically is affected by numerous factors (the presence of other infections, for instance), which in turn creates variation in the observed effectiveness of condoms. Also, ethics get in the way of some of the more effective research designs – if a subject has an STD that's treatable, for example, it's not OK to withhold treatment to see if condom use will keep them from infecting their partners. And there's also the need to control for the fact that often people at lower risk of exposure (e.g., members of monogamous couples) use condoms less regularly than people at higher risk (single people with multiple partners).

OK then. Regarding your first question, Congress was wondering the same thing in 2000 when it ordered the Secretary of Health and Human Services to "reexamine existing condom labels … to determine whether the labels are medically accurate regarding the overall effectiveness or lack of effectiveness of condoms in preventing sexually transmitted diseases, including HPV." Many saw the directive as the work of abstinence-only advocates, but orders are orders. The National Institutes of Health convened a group of experts that year to address the question "What is the scientific evidence on the effectiveness of latex male condom-use [sic] to prevent STD transmission during vaginal intercourse?"

Reviewing the research, the experts concluded (.pdf) that in general it was crappy. Most of the relevant published studies, they found, didn't use the kind of experimental design you'd want to see – i.e., prospective design, in which the researcher compiles data by following the subjects' behavior going forward, rather than gathering data after the fact.

Making do with what they had, the experts divided STDs into three categories: diseases transmitted by sexual secretions, genital ulcer diseases, and HPV (human papilloma virus). Condoms pretty much contain a man's sexual secretions, so you'd figure they'd protect against these diseases best. Genital ulcer diseases mainly spread through sores, though they sometimes also travel via secretions; condoms can't offer complete protection here, because they don't cover some of the areas that could be infectious. HPV gets its own category, as it's "probably transmitted via contact with infected cell surfaces in the presence or absence of fluid or tissue exchange."

The panel found that within the first category, there was good evidence that condoms prevented HIV transmission via vaginal intercourse for both men and women and lowered the risk of gonorrhea for men. But for the other secretion-based STDs – gonorrhea in women, chlamydia, and trichomoniasis – and for the STDs in the other two categories, the panel found there was insufficient evidence to draw any conclusions. It did say, though, that some studies suggested condoms could help in "reducing the risk of HPV-associated diseases, including warts in men and cervical neoplasia in women." The Centers for Disease Control issued a flyer (.pdf) that summarized these findings.

As of March 2004, the FDA was still talking about coming up with draft guidelines, according to spokesman Daniel G. Schultz in testimony before Congress. In November 2005, the FDA issued draft guidance for condom labeling, which repeated the 2001 workshop findings and proposed wording for an insert to go in condom packages:

When used correctly every time you have sex, latex condoms greatly reduce, but do not eliminate, the risk of pregnancy and the risk of catching or spreading HIV, the virus that causes AIDS. Latex condoms can also reduce the risk of other sexually transmitted diseases (STDs), such as chlamydia and gonorrhea, that are spread to or from the penis by direct contact with the vagina and genital fluids.

Condoms provide less protection for certain STDs, including genital herpes and human papallomavirus (HPV) infection, that can also be spread by contact with infected skin outside the area covered by the condom. Condoms cannot protect against these STDs when they are spread in this way. Using latex condoms every time you have sex may still give you some benefits against these STDs. For example, using a condom may lower your risk of catching or spreading genital herpes. Using a condom also may lower your risk of developing HPV-related diseases, such as genital warts and cervical cancer.

So far, though, the FDA has taken no final action to implement its guidance.

Meanwhile, the medical community was working to remedy the lack of useful research. In the 2006 NEJM article quoted above, authors Markus Steiner and Willard Cates surveyed the progress since the workshop and concluded, "Six years later, we have strong evidence that condom use reduces the risk of transmission of HIV, gonorrhea and chlamydia, and herpes simplex virus in both women and men" plus recent evidence that it also helps protect women against HPV. This isn't what the abstinence types wanted to hear, but it's good news for everyone else.

On to question #2. Unprotected oral sex is not risk-free. A July 2007 article in New Scientist reports on research suggesting, for instance, that the tonsils may help transmit HIV during oral sex, although the risk remains much lower than it is for genital intercourse – oral sex leads to HIV infection at most four times in 10,000, while intercourse results in infection once in every 200 to 1,000 cases. But, as the CDC pointed out in 2003, even a relatively low-risk sexual activity can become a significant avenue of STD transmission if people do it often enough, and oral sex does seem to have caught on in a big way.

Two 2006 write-ups in the must-read journal Oral Diseases review the risks of unprotected oral sex. The first, by Dr. George Laskaris, called "Oral Manifestations of Orogenital Bacterial Infections," suggests that both syphilis and gonorrhea are commonly transmitted through oral-genital contact. And in the second, "Oral Viral Infections That Could Be Transmitted Oro-Genitally," Dr. Stina Syrjänen says that viruses meeting her title's admittedly fuzzy criterion include herpes simplex viruses 1 and 2 (HSV-1 and HSV-2), Epstein-Barr virus, cytomegalovirus , human herpesvirus-8, HPV, and HIV. She notes that "receptive oral intercourse" presents a greater HIV risk than experts had once thought, names poor oral health as a contributing factor in HIV transmission, and estimates that "the probability of per act transmission in oral intercourse with ejaculation is 0.04%." She also reports that the "oro-genital route of transmission is more common than expected in genital HSV-1 infections."

In all, while most research in this area focuses on risk to the provider of unprotected oral sex, it's pretty clear that the recipient can also pick up some diseases – HIV, gonorrhea, HSV-1, certain kinds of hepatitis, and possibly syphilis and Epstein-Barr Virus. So while it may be safer in this case to receive than to give, strictly speaking it's not safe.

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Staff Reports are written by the Straight Dope Science Advisory Board, Cecil's online auxiliary. Though the SDSAB does its best, these columns are edited by Ed Zotti, not Cecil, so accuracywise you'd better keep your fingers crossed.

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