In normal condition, there are large amount of bacteria in women's vagina. Because vaginal fluid is acid(pH3-4), those pathogens will not lead to a disease when the environment of vagina is acid. Meanwhile, mucus on cervix uteri also prevent the bacteria from upgoing spread into the pelvic cavity or fallopian tubes.

When menses starts, or infection occurs in vagina, bacteria become active because of the change of pH. Some bacteria would spread upward to the pelvic cavity and causes infection. Pathogens can come from the outside or the body itself. Except for bacteria from the outside( which may spread through sexual intercourses), common bacteria exist in the vagina also would lead to an infection. 　

Causes of PID

- Having too much sexual intercourses or having multiple sexual partners.
- Wound by operation in pelvic cavity.
- Infection when abortion or delivery.
- IUDs.
- Tubercle bacillus infection.
- Bad hygiene during menses, or infection when metrorrhagia occurs.
- Parasite.

Common pathogens of PID

In most cases, the pathogens of PID are various bacteria which would cause fester, e.g. anaerobic streptococcus, hemolytic streptococcus, E.coli, staphylococcus, clostridium perfringens. And most of PID is with multiple infections. Besides, virus can also stir to this disease.

Surveys found that gonococcus is still the most common pathogen of pelvic inflammatory disease. In China, PID caused by gonococcus, chlamydia trachomatis, and trichomonas has a trend of increasing.

Infection approach

1. Bacteria spread upward: pathogens in vagina spread upward and enter the pelvic cavity. The infection can also spread to ovary, fallopian tubes, and the abdominal cavity. It's gonococcus and staphylococcus which causes PID in such a way.

2. Hematogenous spread: bacteria which cause infection in other organs, such as in lung and kidneys, can spread through blood vessels and cause PID or infection in the whole genital system. Often it is a tubercle bacillus infection.

3. Spread by lymphatic system: when bacteria invade the vagina and cervis, they spread through lymphatic system, enter and infect the abdominal cavity.

Streptococcus and staphylococcus often infect women's genital system by this method.

4. Inflammation spread locally: peritonitis, appendicitis, colonitis, bladder infection can also spread locally and cause infection in pelvic cavity.