What is pelvic inflammatory disease?

PID is inflammation in the female upper reproductive tract caused by an infection. The female upper reproductive tract consists of the uterus, fallopian tubes, ovaries, and pelvic peritoneum. Infections that cause PID generally start in the lower reproductive tract (i.e., the vagina or cervix) and spread to the upper reproductive tract.ⁱⁱ

PID prevalence varies by age, with the highest rates consistently occurring among females between the ages of 16 and 24.ⁱⁱⁱ PID is typically caused by sexually transmitted infections (STIs). The most common STIs related to PID are gonorrhea and chlamydia. Barrier methods, like condoms, used to prevent STIs can also help prevent PID.

A 2017 study revealed that 4.4 percent of sexually active females aged 18 to 44 within the U.S. had PID at some point in life.^iv Individuals with certain sexual activity behaviors, such as increased numbers of sexual partners and previous history of an STI, had a higher risk of PID. The authors also observed that the lifetime prevalence of PID was variable depending on socioeconomic factors.^v

What are the symptoms of pelvic inflammatory disease?

Doctors and researchers classify PID into three distinct categories:

• ‍Acute: Sudden onset
• ‍Subclinical: No outwardly observable symptoms
• ‍Chronic: Ongoing

Acute PID

Acute PID symptoms include the sudden onset of lower abdominal pain, severe pain in the pelvic area, foul-smelling or otherwise unusual vaginal discharge, painful sexual intercourse (called dyspareunia), and abnormal vaginal bleeding. Women with acute PID may feel lower abdominal tenderness and/or pain in the cervix during an internal vaginal examination.^vi To check for symptoms of PID, a doctor may insert two fingers into the patient's vagina and use the other hand to press on the lower abdomen to feel for masses or tenderness. Patients with acute PID may also have chills and a high fever above 100.4 degrees F (38 degrees C).^vii

PID patients with severe symptoms can sometimes develop a tubo-ovarian abscess (TOA). This area of inflammation includes a collection of pus, and it forms a mass that involves both the fallopian tube and ovary. A doctor can diagnose TOA with either pelvic ultrasound or computed tomography (CT) imaging of the pelvis.^viii Patients with PID with a tubo-ovarian abscess should be hospitalized to begin intravenous antibiotic treatment. A doctor can also place a minimally invasive drain to help with larger abscesses or if the patient does not improve with intravenous antibiotics.^ix

Subclinical PID

On the other side of the spectrum, some patients may experience minimal or no symptoms, even though they have active inflammation and infection within the upper reproductive tract. This scenario is called subclinical PID and it can still result in adverse long-term consequences.^x Because females without symptoms may not see a doctor right away, subclinical PID is often only diagnosed in cases when a doctor finds scar tissue around a patients’ reproductive organs of the upper genital tract during abdominal surgery.

Chronic PID

Lastly, chronic PID refers to cases of PID caused by Mycobacterium tuberculosis or Actinomyces species with symptoms lasting longer than 30 days.^xi Symptoms of chronic PID may include chronic pelvic pain, abnormal vaginal discharge, and pain with intercourse.

What causes pelvic inflammatory disease?

PID is most commonly caused by STIs, with most cases arising from chlamydia and gonorrhea, though other STIs such as Mycoplasma genitalium and Trichomonas vaginalis (bacterial and parasitic infections) can be the source of PID.^xii

PID caused by gonorrhea tends to be more severe than PID caused by chlamydia. A study of 4,819 patients with PID found that patients with gonorrhea had an 85 percent chance of hospitalization, while patients with chlamydia had a 43 percent chance of hospitalization. Patients testing positive for both chlamydia and gonorrhea had an 87 percent chance of hospitalization.^xiii

While less common, PID can also be caused by the bacteria associated with bacterial vaginosis (BV).^xiv BV is not an STI but is rather a type of vaginal inflammation caused by overgrowth of bacteria that exist naturally in the vagina. Certain microorganisms that can cause BV are also associated with a significantly increased risk of PID.^xv

Another less frequent cause of PID includes infection of the lower reproductive tract by respiratory or enteric (intestinal) pathogens.

Multiple factors put patients at an increased risk for PID:^xvi

• Sexual behaviors that increase the risk of STIs, including having unprotected sex, multiple sex partners, a new sexual partner within three months, a personal history of an STI, or a sex partner with a history of an STI.
• Medical procedures that involve placing an instrument through the cervix and into the uterine cavity, including a dilation and curettage (performed following a miscarriage or to terminate a pregnancy), hysteroscopy or hysterosalpingography (diagnostic tests often performed for infertility), or insertion of an intrauterine device (IUD) for birth control. The use of sterile instruments significantly decreases the risk of infection following these procedures.

While these factors increase the risk of PID, that does not mean that STI infections or infections after medical procedures will always lead to PID.

How is pelvic inflammatory disease diagnosed?

Doctors usually diagnose PID by performing a thorough medical history and physical examination. Sensitivity of clinical diagnosis for PID is approximately 87 percent, meaning the likelihood of a false negative is low.^xvii

A doctor is likely to diagnose a patient with PID if she is at risk for it and has unexplained pelvic pain and cervical, uterine, or ovarian (adnexal) tenderness.^xviii (A female is at risk for PID if she is sexually active or at an increased risk of having an STI.) In this case, treatment may be recommended based on the patient’s symptoms and exam alone.^xix PID can still occur even when STI testing is negative; therefore, laboratory testing alone should not be used to diagnose PID or to determine whether to start antibiotic treatment. Early treatment with antibiotics can prevent severe consequences of PID.

On the other hand, if the patient is not experiencing pain or tenderness, routine STI testing and additional testing are often recommended. Pregnancy tests are also advised before diagnosing PID to rule out a normal (intrauterine) or ectopic pregnancy.^xx

How does pelvic inflammatory disease impact fertility?

Pelvic inflammatory disease may negatively affect female fertility. It most often leads to a condition known as tubal factor infertility (TFI), in which scarring, inflammation, and damage of the fallopian tubes interferes with the ability of sperm, eggs, and embryos to travel through them. Studies suggest 15 to 19 percent of patients with PID develop tubal factor infertility, and multiple episodes of PID increase the risk of developing this type of infertility.^xxi,xxii

Of the bacteria associated with PID, chlamydia infection carries the greatest risk of infertility. The reason may be the inflammatory immune response against Chlamydia trachomatis that occurs in the fallopian tubes during infection.^xxiii

Subclinical PID has also been shown to have adverse effects on fertility. In a study of 418 females, patients with subclinical PID had a 40 percent reduced incidence of pregnancy compared to patients without PID.^xxiv A 2019 study of 121,800 pregnant females (30,450 PID patients and 91,350 matched controls) showed that PID also confers a higher risk of ectopic pregnancy.^xxv Females with PID were just over twice as likely to develop ectopic pregnancy compared to females without PID.^xxvi

What are the treatment options for PID and how successful are they?

PID is treated with antibiotics, most commonly with a combination of ceftriaxone, doxycycline, and metronidazole.^xxvii Ceftriaxone is usually given as an injection, while doxycycline and metronidazole are typically taken as pills for at least 14 days.^xxviii Males who have had sexual contact with a person with PID in the past 60 days should also see their doctor and be treated for possible STIs.^xxix

More severe cases of PID may require hospitalization for administering IV antibiotics, and in more rare cases, for abdominal surgery. The decision to admit a patient to the hospital usually occurs when one of the following conditions is present: pregnancy, surgical emergency, tubo-ovarian abscess, nausea and vomiting with a temperature above 101 degrees F (38.5 degrees C), or when oral antibiotics are not working.^xxx

Early PID treatment may help reduce the risk of long-term complications or serious adverse effects associated with PID. Females should call their doctor as soon as possible after noticing any unusual symptoms.

Since PID can lead to fallopian tube damage, patients who have had pelvic inflammatory disease have an increased risk of infertility and often need help to achieve pregnancy. Tubal factor infertility is most often treated by in vitro fertilization (IVF), which completely bypasses the fallopian tubes. According to the latest national summary data reported by the Society for Assisted Reproductive Technology (SART),^xxxi patients with tubal infertility have a good chance of achieving pregnancy via IVF, with a 44.3 percent cumulative live birth rate per IVF cycle (for females under 35 years old). For comparison, this rate is 41.4 percent in females with other non-tubal factor infertility.^xxxii

In select cases, doctors will use surgery to treat patients with tubal factor infertility. Tubal surgery involves the removal of scar tissue and blockages in or around the fallopian tubes.^xxxiii The decision to use tubal surgery must be balanced against the baseline risks of undergoing the surgical procedure. For older patients or individuals with severe scar tissue around the fallopian tubes, the chance of a successful tubal correction surgery leading to an unassisted pregnancy is generally low, and IVF is the preferred treatment in these cases.

What are the other pelvic inflammatory disease risks/conditions?

PID can lead to several other health risks and possible complications in addition to female infertility:

• ‍Recurrent PID: A clinical trial known as the PEACH (PID Evaluation and Clinical Health) study found that 21.3 percent of females treated for mild to moderate PID experienced recurrence within seven years. PID recurrence was associated with an increased risk of infertility.^xxxiv Reoccurrence can happen if the initial infection was not completely treated or if infection with a new STI or other PID-causing pathogen occurs.
• ‍Chronic pelvic pain: The PEACH study also found that 42 percent of patients treated for PID went on to develop chronic pelvic pain at follow-up.^xxxv
• ^‍Hydrosalpinx: This condition is the accumulation of fluid within and enlargement of the fallopian tubes. Hydrosalpinx can contribute to tubal factor infertility, which can have negative consequences on pregnancy rates and outcomes.^xxxvi

Given the potential for severe outcomes, taking steps to prevent PID is important for all sexually active females. Patients are encouraged to practice safe sex with barrier protection, such as condoms, and regularly get tested (along with any partners) for sexually transmitted infections.

Conclusion

Pelvic inflammatory disease can affect females of all ages, but it most commonly occurs among patients who are at increased risk for contracting a sexually transmitted infection. Though PID is typically caused by STIs, it can also be caused by non-sexually transmitted reproductive tract infections.

Anyone experiencing PID symptoms or concerns about their health should contact their healthcare provider. PID can lead to long-term health problems including infertility and chronic pelvic pain, but prompt treatment may help patients avoid these complications.