Diaphragm and sponge protect against STDs.

The use of diaphragm or contraceptive sponge provides some women with better protection against certain sexually transmitted diseases than does relying on their partner's use of a condom. This new finding may add to the contraceptive options considered by many women, especially those at risk of sexually transmitted diseases (STDs).

"Women have to understand that there are methods they can use independent of their partners that can protect against STDs," says principal investigator Michael J. Rosenberg of the University of North Carolina's School of Public Health in Chapel Hill.

Laboratory studies have shown that an intact condom provides an impermeable barrier to most disease-causing organisms. But despite the condom's prowess in an ideal setting, the device often falls short in the real world.

To find out how the condom stacks up against the diaphragm and the sponge, Rosenberg and his colleagues designed a cross-sectional study of 4,162 women who visited a Denver STD clinic betwen Jan. 1, 1987, and Dec. 31, 1988. The researchers asked the women about the contraceptive device they used most frequently during the month prior to their visit. In addition, laboratory tests identified infections caused by a variety of disease-causing microbes, including Neisseria gonorrhoeae, Trichomonas vaginalis and Chlamydia trachomatis.

These three organisms cause about three-quarters of all cases of STD in the United States, the researchers note. If left untreated, both gonorrhea and chlamydia can cause infertility. Trichomoniasis is a less serious infection that can cause vaginal itching and discharge.

The researchers discovered that women using the contraceptive sponge or the diaphragm had significantly lower rates of gonorrhea and trichomoniasis than did women who relied on their partner's use of a condom. Women using the diaphragm or sponge were also less likely to suffer from chlamydia, although the difference was not statistically significant, the team reports in the May AMERICAN JOURNAL OF PUBLIC HEALTH.

The researchers wanted to get an idea of how people actually use birth control in the real world; however, they admit that they collected very little information on how often women and their partners used contraceptives or whether they used them properly every time.

Rosenberg suspects that women using the diaphragm or the sponge received greater disease protection simply because they used these barrier methods routinely. The spermicide contained in the sponge and applied to the diaphragm before insertion is known to kill disease-causing microbes, he adds.

By contrast, women relying on their partner's use of a condom face a greater risk of disease transmission because the partner may fail to use the device properly or during every act of intercourse, Rosenberg says.

"It is possible that because women are the ones who suffer the most severe consequences from contraceptive failure, they are more likely than men to use their method correctly," he adds.

Noting that STDs spread more easily from men to women than from women to men, Rosenberg recommends that efforts to curb the transmission of these diseases focus on female-controlled contraceptives such as the diaphragm or the sponge. Many women, especially those in high-risk groups, find it difficult to negotiate condom use with their partners, he adds.

The study did not address the question of whether female-controlled methods shield against the virus that causes AIDS, comments Willard Cates Jr. of the Centers for Disease Control in Atlanta. He says the condom, if used properly, still provides the greatest protection against sexually transmitted diseases, including AIDS.