Microbiology

Chlamydia trachomatis and Neisseria gonorrhoea account for the majority of cases. (1)

• Chlamydia is thought to be the most common cause of PID and is associated with 14% to 35% of cases (1)
• Neisseria gonorrhoea and chlamydia trachomatis co-infection can occur

Less commonly, PID may result from: (2)

• Mycoplasma hominis
• Mycoplasma genitalium
• anaerobes such as Bacteroides
• G. vaginalis
• Haemophilus influenzae
• Cytomegalovirus
• U. urealyticum
• Actinomyces israelii - especially with long term IUCD; may cause unilateral infection
• Herpes simplex virus type II - very rarely

No microbiological cause can be found in 20%.

Routes of infection include:

• ascending from the vagina - endogenous infection, for example, Bacteroides; or sexually transmitted infection, especially Chlamydia and Neiserria
  
  
• direct inoculation - for example, during dilatation and curettage, termination of pregnancy, insertion of a intrauterine contraceptive device
  
  
• transperitoneal - for example, following appendicitis or diverticulitis
  
  
• haematogenous - classically tuberculosis, usually at the time of puberty, but theoretically, any bacteraemia may produce pelvic foci of infection

Reference:

1. Goller JL et al. Population attributable fraction of pelvic inflammatory disease associated with chlamydia and gonorrhoea: a cross-sectional analysis of Australian sexual health clinic data. Sex Transm Infect. 2016 Nov;92(7):525-31.

2. Curry A, Williams T, Penny ML. Pelvic Inflammatory Disease. Diagnosis, Management, and Prevention. Am Fam Physician. 2019 Sep 15;100(6):357-364.