Causes of pelvic inflammatory disease

Pelvic inflammatory disease (PID) is caused by an infection developing in the female upper genital tract.

In most cases, the condition is caused by a bacterial infection spreading from the vagina or cervix (the entrance to the womb) into the womb, fallopian tubes and ovaries.

PID is often caused by more than one type of bacterium and it can sometimes be difficult for doctors to pinpoint which are responsible. Therefore, a combination of antibiotics will be prescribed so that a variety of bacteria can be treated.

Sexually transmitted infections (STIs)

In about one in every four cases, PID is caused by a sexually transmitted infection (STI) such as chlamydia or gonorrhoea.

These bacteria usually only infect the cervix (neck of the womb), where they can be easily treated with a single dose of an antibiotic.  However, if they are not treated there is a risk that the bacteria could travel into the upper genital tract.

It is estimated that one in 10 women with untreated chlamydia may develop PID within a year.

Other causes

In many cases, the cause of the infection that leads to PID is unknown. Such cases may be due to normally harmless bacteria found in the vagina. These bacteria can sometimes get past the cervix and into the reproductive organs. Although harmless in the vagina, these types of bacteria can cause infection in other parts of the body.

Infection in this way is most likely to happen if you have had PID before, if there has been damage to the cervix following a miscarriage or childbirth, or if you have a procedure that involves opening the cervix, such as an abortion, inspection of the womb, or insertion of an intrauterine contraceptive device (coil).

Which areas can become infected?

If an infection spreads upwards from the vagina and cervix (entrance to the womb), it can cause inflammation of the:

  • womb lining (endometrium)
  • fallopian tubes
  • tissue around the womb
  • ovaries
  • lining of the inside of the abdomen (peritoneum)

Pockets of infected fluid, called abscesses, can also develop in the ovaries and fallopian tubes.