Causes of pelvic inflammatory disease.

Key takeaways

• Article type classification: sexual_health.
• PID usually develops when bacteria travel upwards from the vagina or cervix into the upper reproductive tract.
• This article focuses on sexually transmitted and non-STI bacteria, risk factors, IUD timing, recurrent infection and prevention.
• Mayo Clinic’s PID condition page was used as the minimum completeness benchmark for symptoms, causes, risk factors, complications and prevention.
• Use NHS 111 for urgent advice or call 999 in a life-threatening emergency, especially with severe pelvic pain, fainting, suspected ectopic pregnancy, sepsis symptoms or severe illness.

Overview

Pelvic inflammatory disease, usually called PID, is infection and inflammation affecting the upper female reproductive tract. It can involve the womb lining, fallopian tubes, ovaries and surrounding pelvic tissues. It often follows bacteria moving upwards from the vagina or cervix, but it is not always caused by one identifiable sexually transmitted infection.

The most common route is ascending infection. Bacteria first infect or colonise the cervix or vagina, then move upwards into the womb lining, fallopian tubes, ovaries or surrounding pelvic tissues. BASHH guidance says gonorrhoea and chlamydia account for a proportion of UK cases, but vaginal anaerobes and Mycoplasma genitalium may also be involved. This is why a negative chlamydia or gonorrhoea result does not automatically exclude PID.

PID risk can rise after a recent STI, a new sexual partner, multiple partners, a partner with an STI, previous PID or recent instrumentation of the womb. BASHH notes that IUD insertion increases PID risk mainly in the first few weeks after insertion, particularly where an existing infection is present. PID can also occur without a current STI because the upper reproductive tract can be affected by mixed bacteria.

This is a sexual-health topic, but it should never be written with blame. PID can affect people with different relationship histories, and symptoms may be missed because pelvic pain, bleeding and discharge have many possible causes. The safest message is early assessment, appropriate tests, treatment when indicated and partner management where an STI may be involved.

Symptoms and reader concerns

NHS guidance describes PID symptoms such as pain around the lower tummy or pelvis, discomfort or pain during sex felt deep inside the pelvis, pain when passing urine, bleeding between periods or after sex, heavy or painful periods, unusual vaginal discharge and sometimes fever, nausea or vomiting. BASHH adds bilateral lower abdominal pain, cervical motion tenderness, adnexal tenderness and abnormal vaginal or cervical discharge as important clinical features.

Symptoms can be subtle. Some people have mild discomfort, intermittent bleeding or discharge rather than dramatic pain. Others become severely unwell. PID can overlap with ectopic pregnancy, appendicitis, ovarian cyst torsion or rupture, endometriosis, urinary infection and bowel conditions, so assessment should not rely on self-diagnosis.

Readers often worry about fertility, pain during sex, whether a partner has been unfaithful or whether an IUD caused the infection. The answer depends on the individual situation. A clinician can test for STIs, assess pregnancy possibility, examine the pelvis, consider ultrasound and decide whether treatment should start before all results return.

Causes and risk factors

PID usually happens when bacteria ascend from the cervix or vagina into the upper reproductive tract. Chlamydia and gonorrhoea are important causes, but mixed vaginal bacteria, anaerobes and Mycoplasma genitalium can also be involved. This mixed-bacteria picture is why broad-spectrum antibiotic treatment may be used and why STI tests do not explain every case.

Risk factors include age under 25, a recent new sexual partner, more than one sexual partner, a partner with an STI, previous PID, recent chlamydia or gonorrhoea, and sex without barrier protection. Risk can also be higher in the weeks after IUD insertion if infection was already present. Having PID does not prove any one cause; it means bacteria have reached tissues where they can cause inflammation and scarring.

At tissue level, infection triggers inflammation in the womb lining and fallopian tubes. Swelling, pus, inflammatory cells and healing tissue can disrupt the fine cilia and delicate tube structure that normally help an egg move towards the womb. If inflammation is severe or recurrent, scarring and adhesions can form, which explains the link between PID, ectopic pregnancy risk and fertility problems.

Diagnosis and tests

There is no single perfect PID test. Diagnosis is usually based on symptoms, sexual history, pregnancy testing, pelvic examination and swabs or urine tests for STIs. BASHH guidance notes that symptoms and signs lack sensitivity and specificity, so clinicians may treat on clinical suspicion when the pattern fits and pregnancy has been excluded.

Tests may include chlamydia, gonorrhoea and sometimes Mycoplasma genitalium testing, a pregnancy test, urine testing, blood tests for inflammation, and ultrasound if an abscess, ectopic pregnancy, ovarian cyst or another cause is possible. A positive STI test supports the diagnosis, but a negative result does not rule it out.

Pelvic examination can feel exposing or uncomfortable, so clinicians should explain what they are doing and obtain consent. It may identify cervical motion tenderness, uterine tenderness, adnexal tenderness, discharge or bleeding. If pain is severe, pregnancy is possible or a surgical emergency cannot be excluded, urgent assessment is needed.

Treatment and partner care

PID is usually treated with antibiotics that cover likely organisms. Treatment should be taken exactly as prescribed, and symptoms should be reviewed if they do not improve. BASHH recommends a low threshold for empirical treatment because delaying treatment may increase long-term complications. Some people need hospital assessment, intravenous antibiotics, observation or drainage of an abscess.

Partner care matters. Current and recent sexual partners may need testing and treatment, especially for chlamydia or gonorrhoea. Avoid sex, including condomless sex, until treatment is completed and a clinician says it is safe, because reinfection can occur. If an STI is confirmed, partner notification is part of protecting both partners and future partners.

People who are pregnant, very unwell, unable to tolerate tablets, have a suspected tubo-ovarian abscess, have severe pain or do not improve after treatment may need specialist or hospital care. Treatment choices should be made by a clinician because antibiotic selection depends on pregnancy status, local resistance patterns, allergy history and likely organisms.

Complications and fertility

Possible complications include chronic pelvic pain, recurrent PID, tubo-ovarian abscess, ectopic pregnancy and fertility problems. The risk is not the same for everyone. It can be influenced by how quickly treatment starts, how severe the infection is, whether infection recurs and whether the fallopian tubes are damaged.

Fertility concerns deserve sensitive discussion. Many people conceive after PID, but previous PID can increase the chance of tubal-factor fertility difficulty or ectopic pregnancy. Seek medical advice promptly if you have a positive pregnancy test after PID and develop one-sided pelvic pain, shoulder-tip pain, dizziness, fainting or bleeding, because ectopic pregnancy can be an emergency.

Self-care and prevention

Self-care supports medical treatment but does not replace it. Rest if symptoms are significant, use pain relief as advised by a clinician or pharmacist, drink fluids, complete antibiotics and attend follow-up. Do not rely on vaginal washes, supplements or home remedies to treat PID; they will not clear an upper reproductive tract infection.

Prevention focuses on STI testing, prompt treatment of chlamydia or gonorrhoea, condom use with new or casual partners, partner notification and attending sexual-health services when symptoms appear. Before IUD insertion, clinicians may ask about STI risk or offer testing where appropriate. If symptoms develop after insertion, seek advice rather than removing anything yourself.

When to seek medical advice

Contact a GP or sexual-health clinic if you have lower pelvic pain, pain during sex, unusual discharge, bleeding between periods or after sex, pain when passing urine, fever, or a recent STI exposure. Seek prompt care if symptoms are worsening, you might be pregnant, or you have had PID before.

Use NHS 111 for urgent advice if pelvic pain is significant and you are unsure where to go. Call 999 or seek emergency care for severe sudden pain, fainting, shoulder-tip pain with possible pregnancy, confusion, signs of sepsis, severe vomiting, collapse or any life-threatening emergency.

Sources

• NHS, Pelvic inflammatory disease: https://www.nhs.uk/conditions/pelvic-inflammatory-disease-pid/
  Relevance: Supports UK-facing PID symptoms, causes, diagnosis, treatment, partner advice and complications.
• BASHH, PID 2019 guideline: https://www.bashh.org/resources/6/pid_2019/
  Relevance: Supports specialist UK sexual-health guidance on PID aetiology, clinical features, diagnosis, management, follow-up and partner notification.
• Mayo Clinic, pelvic inflammatory disease symptoms and causes: mayoclinic.org guidance page link unavailable during validation (mayoclinic.org guidance page, link unavailable during validation)
  Relevance: Used as the Mayo-depth benchmark for PID symptoms, risk factors, complications and prevention coverage.
• CDC, Pelvic Inflammatory Disease STI Treatment Guidelines: https://www.cdc.gov/std/treatment-guidelines/pid.htm
  Relevance: Supports diagnostic uncertainty, broad-spectrum treatment principles and the importance of early treatment to reduce reproductive complications.
• NHS, when to use NHS 111: https://www.nhs.uk/nhs-services/urgent-and-emergency-care-services/when-to-use-111/
  Relevance: Supports urgent-care signposting when symptoms are severe, rapidly worsening or confusing.

Disclaimer

Educational only. Results vary. Not a cure.