Biologic sexism of STIs


On any given day, 1 in 5 people has a sexually transmitted infection.[1] It is not unlikely that one of the infected will be seeing you for treatment. Most RTIs exhibit a “biological sexism,” say Jeanne Marrazzo and Ina Park.[2] Women are more likely than men to acquire RTIs, due to the transmission dynamics during an act of vaginal intercourse. For example, the risk of acquiring gonorrhea from a single act of vaginal intercourse (where one partner is infectious) is approximately 25% for men and 50% for women. The risk of acquisition increases when trauma occurs to the genital mucosa, as may be the case in sexual assault. For similar reasons, the risk increases from anal intercourse (a risk that also affects men who receive anal penetration). RTI acquisition is less likely during oral sex, digital penetration, or sex acts other than vaginal or anal intercourse.

Compared with men, women suffer more severe long-term consequences, including PID, infertility, ectopic pregnancy, chronic pelvic pain, and cervical cancer. Women may also be less likely to seek health care for assessment of RTI-related symptoms, because a higher proportion of their RTIs are asymptomatic or unrecognized as being serious. The probability of suffering consequences from an RTI, say Marrazzo and Park, depends on whether or not a patient receives proper diagnosis and treatment.

The probability that unprotected sexual intercourse will lead to RTIs or their consequences differs from the probability of unintended pregnancy. (See Table.) The risk of pregnancy varies according to the menstrual cycle. In contrast, while numerous complex factors probably modulate susceptibility to RTI:[1],[2]

  • having sex with an infected person
  • the gender of the infected person
  • transmissibility of the particular RTI
  • use of barriers or other protective measures

In the case of HIV, the quantity of serum (and presumably genital) HIV viral load directly influences risk of transmitting HIV to vulnerable partners. HIV viral load is extremely high in the context of early infection (the first several months after a person acquires the virus). Because sexual transmission of HIV frequently occurs during this early infection interval,[3] persons at risk need to consider HIV-prevention methods at all times.

Comparative risk of adverse consequences from vaginal or anal intercourse: RTI and unintended pregnancy

Unintended pregnancy (per coital act)[4]
  • 17%–30% midcycle
  • < 1% during menses
HIV transmission (per coital act)
  • 0.08% receptive vaginal sex
  • 0.04% insertive vaginal sex
  • 1.3% receptive anal sex
  • 0.11% insertive anal sex
Gonococcal transmission (per coital act)[5]
  • 50% receptive vaginal sex
  • 25% insertive vaginal sex
PID per woman infected with cervical chlamydia[6]
  • 22% if not treated
  • 0% if promptly and adequately treated
Tubal infertility per PID episode[7]
  • 8% after first episode
  • 20% after second episode
  • 40% after third or more episodes

Different individuals accept different levels of risk. Not everyone will follow every safer sex recommendation but, with the proper knowledge, each person can make his or her own informed choices about reducing risk. Some prevention messages are universal and should be reinforced (for example, barrier methods when appropriate). Additionally, client-centered counseling highlights the need to individualize risk assessment and tailor risk-reduction plans. The latter may include a discussion on selecting sex partners and building skills for negotiating safer sex.

Be sure to make your guidance specific to related to an individual’s particular issues, rather than giving vague, global advice, Marrazzo and Park inform us:

  • “Starting today, put condoms on the night stand beside the bed,” rather than “always use condoms.”
  • “You could reconsider whether to date this person, who is also dating other people,” rather than “Have fewer, safer partners.”
  • “Next time you’re out with friends and might have sex, avoid getting high on drugs or alcohol,” rather than “Have safer sex.”

Now stop for a minute as you reach the end of this article. Accept that your patients, and in many cases, you, the health care clinician, may have some reservation or feelings of awkwardness over holding these kinds of conversations. As Ina Park states in her book Strange Bedfellows: Adventures in the science history and surprising secrets of STDs, “…even with the ubiquity of STIs…most people (even health care providers) simply don’t feel comfortable discussing them. For most of us, having sex is much easier than talking about sex, especially its least pleasant consequences.”[8]

So how do you, we, go about discussing these sensitive and private topics? Park writes, “I don’t know, but we must start somewhere. We’ve managed to defeat stigma surrounding previously taboo subjects such as cancer, creating discourse and shifting public sentiment toward support rather than shame. We need similar sea change around STIs to have any hope of curbing the current epidemic.”

We must start somewhere, as Park says. Let’s start here.


[2] Marrazzo JM, Park IU. Reproductive tract infections,including HIV and other sexually transmitted infections.

[1] Cates W, Jr. Review of non-hormonal contraception (condoms, intrauterine devices, nonoxynol-9 and combos) on HIV acquisition. J Acq Imm Def 2005;38 Suppl 1:S8–10.

[2] Garnett G. The transmission dynamics of sexually transmitted infections. In: Holmes KK, Sparling PF, Stamm WE, et al., eds. Sexually transmitted diseases. 4th ed. New York: McGraw-Hill; 2008:27–39.

[3] Pilcher CD, Tien HC, Eron JJ, Jr., et al. Brief but efficient: acute HIV infection and the sexual transmission of HIV. J Infect Dis 2004;189:1785–92.

[4] Trussell J, Kost K. Contraceptive failure in the United States: a critical review of the literature. Stud Fam Plann 1987;18:237–83.

[5] Garnett G. The transmission dynamics of sexually transmitted infections. In: Holmes KK, Sparling PF, Stamm WE, et al., eds. Sexually transmitted diseases. 4th ed. New York: McGraw-Hill; 2008:27–39.

[6] Herzog SA, Heijne JC, Althaus CL, Low N. Describing the progression from Chlamydia trachomatis and Neisseria gonorrhoeae to pelvic inflammatory disease: systematic review of mathematical modeling studies. Sex Transm Dis 2012;39:628–37.

[7] Westrom L, Joesoef R, Reynolds G, Hagdu A, Thompson SE. Pelvic inflammatory disease and fertility. A cohort study of 1,844 women with laparoscopically verified disease and 657 control women with normal laparoscopic results. Sex Transm Dis 1992;19:185–92.

[8] Park I. Strange Bedfellows: Adventures in the science history and surprising secrets of STDs. New York: Flatiron Books, 2021, p. 5.