Is Pelvic Inflammatory Disease a Polymicrobial Infection?
Yes, pelvic inflammatory disease is definitively a polymicrobial infection in the majority of cases, with most PID involving multiple organisms rather than a single pathogen. 1, 2
Microbial Composition of PID
Primary Sexually Transmitted Pathogens
- Neisseria gonorrhoeae and Chlamydia trachomatis are the primary sexually transmitted organisms that initiate PID, with cervical isolation rates of 27-80% for gonorrhea and 5-39% for chlamydia 1
- However, these organisms alone do not account for the full spectrum of PID cases, as 10-40% of untreated cervical infections with these pathogens progress to symptomatic upper genital tract disease 2, 3
Polymicrobial Nature
- A wide variety of anaerobic and aerobic bacteria are isolated from the upper genital tracts of 25-50% of women with acute PID, occurring alongside or independent of the sexually transmitted pathogens 1
- The most common anaerobic bacteria include Bacteroides, Peptostreptococcus, and Peptococcus species 1
- The most common facultative (aerobic) bacteria include Gardnerella vaginalis, Streptococcus species, Escherichia coli, and Haemophilus influenzae 1
Role of Bacterial Vaginosis
- Bacterial vaginosis serves as an antecedent condition that leads to polymicrobial acute PID 1
- The organisms involved in bacterial vaginosis are similar to the nongonococcal, nonchlamydial bacteria frequently isolated from the upper genital tract of women with acute PID 1, 3
Clinical Implications of Polymicrobial Etiology
Treatment Considerations
- Because of the polymicrobial nature of PID, treatment must include broad-spectrum antibiotic regimens that provide adequate coverage against N. gonorrhoeae, C. trachomatis, anaerobes, gram-negative facultative bacteria, and streptococci 4, 5, 6
- Single-agent therapy targeting only one pathogen is insufficient and may allow persistent infection 5, 7
Bacterial Synergy
- Synergistic relationships exist between organisms in PID, particularly between N. gonorrhoeae and Bacteroides fragilis, where the growth of each component is enhanced when present together 8
- This synergy enables organisms to cause more severe local and systemic damage to the host 8
Common Pitfalls to Avoid
- Do not assume PID is caused by a single pathogen based on cervical culture results alone - fallopian tube sampling shows different organisms than cervical cultures, with gonorrhea isolated from tubes in only 13-18% of cases despite higher cervical isolation rates 1
- Do not use narrow-spectrum antibiotics targeting only gonorrhea or chlamydia - this approach fails to address the polymicrobial nature and may lead to treatment failure and sequelae development 4, 5
- Recognize that even when N. gonorrhoeae is recovered from the cervix, it is less commonly recovered from intra-abdominal sites, suggesting other organisms play a significant role in upper tract infection 8