There are two major causes of STDs/STIs:
- Bacteria, including chlamydia, gonorrhea, and syphilis
- Viruses, including HIV/AIDS, genital herpes, genital warts, human papilloma virus (HPV), hepatitis B virus, and cytomegalovirus (pronounced sahy-toh-MEG-uh-loh-vahy-ruhs)
Occasionally, yeasts and protozoan parasites, such as Trichomonas vaginalis (pronounced TRIK-uh-MOH-nuss vaj-uh-NAHY-lis), crab lice, or scabies, cause STDs/STIs.1
Any STD/STI can be spread through sexual intercourse, and some STDs/STIs also are spread through oral sex and sex play. Ejaculation does not have to occur for an STD/STI to be passed from person to person. Sharing contaminated needles used to inject drugs or using contaminated body piercing and tattooing equipment also can transmit some infections, such as HIV or hepatitis B and C.
A few diseases (such as cytomegalovirus and molluscum contagiosum) can be sexually transmitted but are also spread through nonsexual, close contact. Regardless of how a person is exposed, once a person is infected by an STD/STI, he or she can spread the infection to other people through oral, vaginal, or anal sex, even if he or she has no symptoms.
STDs/STIs are of particular concern in pregnant women, because some infections can be passed on to the infant before birth or during delivery. However, the risk of transmission from mother to infant can be lowered, and it is important for every expectant mother to be screened.
For example, a pregnant woman with HIV can pass the virus to her infant before birth, during delivery, and through breastfeeding. This transmission can be prevented through treatment with certain medications during pregnancy and near delivery. After birth, women who have HIV should refrain from breastfeeding their infants if safe alternatives, such as infant formula, are available, further reducing the infant's risk.2
In other cases, if the mother has an infection such as gonorrhea, herpes, or cytomegalovirus, in which risks of transmission are high during delivery, other steps can be taken to reduce the likelihood that the infant will be infected. In these instances, health care providers can treat the pregnant woman for the STD/STI before birth, or the infant can be delivered by cesarean section (also referred to as C-section).2
- Illinois Department of Public Health. Facts about vaginitis and vaginal infections. Retrieved June 27, 2012, from http://www.idph.state.il.us/about/womenshealth/factsheets/vag.htm [top]
- The American College of Obstetricians and Gynecologists. (2011, May) Frequently asked questions. HIV and pregnancy. Retrieved June 27, 2012, from http://www.acog.org/~/media/For%20Patients/faq113.pdf?dmc=1&ts=20120711T1503446877 [top]