The same organisms responsible for bacterial sexually transmitted diseases (such as chlamydia, gonorrhea, mycoplasma, staph, strep) cause 90% to 95% of all cases of pelvic inflammatory disease (PID). Although sexual transmission is the most common cause of PID, bacteria may enter the body after gynecological events or procedures such as IUD insertion (intrauterine device used for contraception), childbirth, spontaneous abortion (miscarriage), therapeutic or elective abortion, and endometrial biopsy.

In the United States, nearly 1 million women develop PID each year. It is estimated that 1 in 8 sexually active adolescent girls will develop PID before reaching age 20. Since PID is frequently underdiagnosed, statistics are probably greatly underestimated.

Risk factors include sexual activity during adolescence, multiple sexual partners, a past history of PID, a past history of any STD (sexually transmitted disease), and the use of non-barrier type contraceptives. Use of an IUD (intrauterine device) may increase the risk of developing PID at the time of IUD insertion.

Oral contraceptives ("the pill") are thought in some cases to enhance cervical ectropion, a condition that allows easier access to tissue where bacteria may thrive. However, oral contraceptives may in other cases have a protective role against developing PID because they stimulate the body to produce a thicker cervical mucous, which is harder for semen (which may contain bacteria) to penetrate. This makes it harder for semen to transmit bacteria to the uterus.

The most common symptoms of PID include:

• vaginal discharge with abnormal color, consistency or odor
• abdominal pain either localized or generalized
• fever (not always present)
  • may range from transient to constant
  • low grade to high

Other nonspecific symptoms that may be seen with PID include:

• chills
• irregular menstrual bleeding or spotting
• increased menstrual cramping
• menstruation, absent
• increased pain during ovulation
• sexual intercourse, painful
• bleeding after intercourse
• low-back pain
• fatigue
• lack of appetite
• nausea, with or without vomiting
• frequent urination
• pain with urination
• point tenderness

Note: There may be no symptoms. People who experience ectopic pregnancies (pregnancies where the embryo implants in the fallopian tubes instead of the uterus) or infertility are often found to have so-called "silent" PID, which is usually caused by chlamydia infection.

• a WBC
• an ESR (sed rate)
• a wet prep or wet mount microscopic examination
• a serum HCG (pregnancy test)
• an endocervical culture for gonorrhea, chlamydia, or other organisms
• a laparoscopy (may be needed)
• pelvic ultrasound or CT scan (may be needed)

• 15% risk of infertility following the 1st episode of PID
• 30% risk of infertility following 2 episodes of PID
• 50% risk of infertility following 3 or more episodes of PID

Preventive measure include following safer sex behaviors; following the health care provider's recommendations after gynecological events or procedures; and getting prompt treatment for sexually transmitted diseases. Sexual partners should also get adequate treatment.

The risk of PID can be reduced by getting regular STD screening exams, and by couples being tested before initiating sexual relations. Testing can detect STDs that may not be producing symptoms yet.