What causes pelvic inflammatory disease?

It is usually caused by microorganisms, most often the sexually transmitted bacteria Chlamydia trachomatis and Neisseria gonorrhoeae, ascending from the cervix and vagina into the uterus and fallopian tubes; the infection is frequently polymicrobial.

Why is PID linked to infertility?

Inflammation of the fallopian tubes can damage their lining and cause scarring or blockage, which interferes with the passage of the egg and sperm and raises the risk of tubal-factor infertility and ectopic pregnancy.

Can PID occur without obvious symptoms?

Yes. A substantial proportion of PID is mild or subclinical, meaning tubal damage can accumulate even without a clearly recognised acute illness.

Pelvic Inflammatory Disease

Pelvic inflammatory disease (PID) is an infection and inflammation of the upper female genital tract, involving some combination of the endometrium, fallopian tubes, ovaries, and surrounding pelvic peritoneum. It usually results from microorganisms ascending from the cervix and vagina, and it is clinically important because tubal inflammation can leave lasting damage that affects fertility.

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Definition

Pelvic inflammatory disease is an acute or subacute infectious inflammation of the upper female genital tract — endometrium, fallopian tubes, ovaries, and pelvic peritoneum — typically caused by microorganisms ascending from the lower genital tract.

Scope

The entry covers what PID is, how lower genital tract pathogens ascend to cause upper-tract infection, the spectrum from subclinical to acute disease, the syndromes it encompasses (endometritis, salpingitis, tubo-ovarian abscess), and its long-term reproductive sequelae. It is a reference description of the entity and its mechanisms, not a guide to diagnosis or treatment.

Core questions

Which pathogens cause PID and how do they reach the upper genital tract?
Why is PID often clinically silent yet still capable of causing tubal damage?
How does tubal inflammation translate into infertility and ectopic pregnancy?
What is the spectrum of disease from endometritis to tubo-ovarian abscess?

Key concepts

Ascending infection from the lower genital tract
Polymicrobial aetiology
Chlamydia trachomatis and Neisseria gonorrhoeae as primary pathogens
Endometritis, salpingitis, and tubo-ovarian abscess
Subclinical (silent) PID
Tubal-factor infertility
Ectopic pregnancy and chronic pelvic pain as sequelae

Mechanisms

PID most often begins when sexually transmitted pathogens — chiefly Chlamydia trachomatis and Neisseria gonorrhoeae — infect the cervix and then ascend through the endometrial cavity to the fallopian tubes; organisms from the vaginal flora and, in some cases, Mycoplasma genitalium also contribute to the polymicrobial picture (Brunham, 2015; Lis, 2015). Inflammation of the tubal mucosa damages the ciliated epithelium and can lead to scarring, adhesions, and tubal occlusion. This anatomical damage is the mechanistic link between an episode of infection and later impairment of fertility, even when the original infection produced few or no symptoms (Brunham, 2015).

Clinical relevance

PID matters because the inflammation it causes in the fallopian tubes can persist after the infection resolves, contributing to tubal-factor infertility, ectopic pregnancy, and chronic pelvic pain; a substantial proportion of cases are mild or subclinical, so damage can accumulate without a clearly recognised acute illness (Westrom, 1992; Brunham, 2015). This description explains why the entity is regarded as consequential; it is not a basis for self-diagnosis or for individual management decisions.

Epidemiology

PID is a common complication of lower genital tract sexually transmitted infection in reproductive-age women, and the risk of adverse reproductive outcomes rises with the number and severity of episodes. The classic cohort study by Westrom and colleagues documented markedly increased rates of tubal infertility and ectopic pregnancy following laparoscopically confirmed disease (Westrom, 1992).

Evidence & guidelines

Contemporary reviews summarise the microbiology, clinical spectrum, and reproductive consequences of PID (Brunham, 2015), and the CDC Sexually Transmitted Infections Treatment Guidelines provide the reference diagnostic and management framework used in practice (Workowski, 2021). Evidence on the role of Mycoplasma genitalium has been synthesised in meta-analysis (Lis, 2015). This entry reports these sources for orientation rather than reproducing their clinical recommendations.

Debates

How important is Mycoplasma genitalium as a cause of PID?: Beyond the established roles of Chlamydia trachomatis and Neisseria gonorrhoeae, the contribution of Mycoplasma genitalium to upper genital tract disease has been increasingly recognised; meta-analysis links it to female reproductive tract disease, though its precise weight and management implications remain under study.

Seminal works

brunham-2015
westrom-1992
workowski-2021

Frequently asked questions

What causes pelvic inflammatory disease?: It is usually caused by microorganisms, most often the sexually transmitted bacteria Chlamydia trachomatis and Neisseria gonorrhoeae, ascending from the cervix and vagina into the uterus and fallopian tubes; the infection is frequently polymicrobial.
Why is PID linked to infertility?: Inflammation of the fallopian tubes can damage their lining and cause scarring or blockage, which interferes with the passage of the egg and sperm and raises the risk of tubal-factor infertility and ectopic pregnancy.
Can PID occur without obvious symptoms?: Yes. A substantial proportion of PID is mild or subclinical, meaning tubal damage can accumulate even without a clearly recognised acute illness.