What Are the Causes of Pelvic Inflammatory Disease?

Pelvic inflammatory disease (PID) is an infection that occurs when microorganisms travel from the lower genital tract—the vagina and cervix—to the upper genital tract, which includes the uterus, ovaries and fallopian tubes.

Approximately 2.5 million women ages 18 to 44 nationwide have self-reported a diagnosis of PID in their lifetime, according to a 2107 report published by the Centers for Disease Control and Prevention (CDC), based on data collected in 2013 and 2014. Also, about 1 in 8 women with a history of PID experience difficulties getting pregnant.

Those numbers may be higher. University of Florida Health noted that nearly 1 million women in the United States have PID each year. About 1 in 8 sexually active girls will develop PID before age 20.

Indeed, pelvic inflammatory disease is seen most often in sexually active young women. The signs are not obvious, however, and almost 70 percent of PID cases in the adolescent population are diagnosed in the emergency department, according to a 2011 report.

Learning the causes of PID, such as sexually transmitted infections (STIs) and diseases (STDs), can help you prevent this painful infection.

What is pelvic inflammatory disease?

Part of the problem with diagnosing PID is a lack of symptoms. Not every case of pelvic inflammatory disease starts with obvious symptoms. Some women don't realize they have a problem until they have issues becoming pregnant.

Untreated pelvic inflammatory disease can lead to a painful infection that requires antibiotics and, sometimes, hospitalization.

Common symptoms of pelvic inflammatory disease include the following:

• Fever
• Pain after sexual intercourse
• Painful urination
• Sharp pain in the upper or lower abdomen

What are the causes of pelvic inflammatory disease?

Our knowledge of PID has grown over the years as technology advanced, testing became more accurate and the prevalence of pathogens increased.

In the 1950s, researchers thought tuberculosis or gonorrhea caused pelvic inflammatory disease. By the 1980s, they attributed most cases to gonorrhea. However, gonorrhea or chlamydia is present in only one-quarter to one-third of PID cases, according to a 2021 report.

Three groups of pathogens are associated with PID, the report suggested. These include the following:

1. Sexually transmitted organisms such as Neisseria gonorrhea (N. gonorrhea), Chlamydia trachomatis or Trichomonas vaginalis
2. Bacteria associated with bacterial vaginosis, such as Atopobium vaginae, BVAB3 (bacterial vaginosis) or Prevotella bivia
3. Gastrointestinal or respiratory bacteria such as E. coli or Haemophilus influenzae

STDs as a cause of pelvic inflammatory disease

Gonococcal pelvic inflammatory disease—an infection affecting the cervix—is the result of gonorrhea. According to a 2021 report, researchers identified it as the "infectious cause" of PID after gonococci were first isolated from the fallopian tubes of a woman with acute salpingitis in 1886.

Since then, N. gonorrhea has been isolated from the fallopian tubes, endometrium and peritoneal fluid in women, according to the same report. It is not always coupled with a recognizable cervical infection, however.

N. gonorrhoeae and Chlamydia trachomatis are not the only sexually transmitted organisms that can cause PID.

Mycoplasma genitalium is often associated with pelvic inflammatory disease, but its relationship with the female genital tract is less clear. Patients reported similar symptoms as with chlamydial PID, but those with Mycoplasma genitalium (Mgen) were less likely to report bleeding after sex and more likely to have tenderness in the lower abdominal area.

The organism Trichomonas vaginalis (TV) can cause vaginitis (the inflammation of the vagina), lesions and acute inflammatory disease of a mucous layer of the genitals, or genital mucosa. Despite this, it is not a widely accepted cause of pelvic inflammatory disease.

TV is rarely isolated in tissue specimens of the upper genital tract. Researchers have noted, however, that changes in the endometrium due to TV, Chlamydia trachomatis and N. gonorrhoeae appear indistinguishable.

Some researchers believe T. vaginalis may affect pelvic inflammatory disease more than previously thought.

Bacterial vaginosis and its association with PID

Women have bacteria in their genitals, and that's normal. An optimal vaginal microbiome helps protect against infection and colonization by harmful bacteria. Disruptions to the microbiome can lead to various vaginal health conditions such as bacterial vaginosis (BV).

Bacterial vaginosis can lead to adverse effects, including an increased risk of infertility, STIs and pelvic inflammatory disease.

Bacterial vaginosis is a lower genital tract disease, and pelvic inflammatory disease is an upper genital tract disease. So how does BV potentially lead to PID?

When these anaerobes—microorganisms that don't require oxygen for survival—ascend the genital tract from the vagina in less than 30 days, this movement causes acute PID. According to a 2015 report, when it takes longer than 30 days, it becomes chronic endometritis.

The same report noted that more than 85 percent of PID cases were due to BV-related bacteria and other STIs.

Gastrointestinal and respiratory organisms that cause PID

Organisms such as E. coli and Haemophilus influenzae are associated with pelvic inflammatory disease.

It's difficult for medical professionals to determine whether these organisms cause PID or whether they take advantage of an altered environment in the upper genital tract to cause an infection.

The bottom line

Pelvic inflammatory disease has various causes. It's vital to pay attention to your body because leaving PID untreated can cause health complications, including infertility.

Any scarring or damage to the reproductive tract that pelvic inflammatory disease might cause cannot be undone. Early diagnosis and treatment using antibiotics can be effective in preventing such damage. See your healthcare professional to learn more.