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Pathogenesis of and risk factors for pelvic inflammatory disease

Charles H Livengood, III, MD
Section Editor
Noreen A Hynes, MD, MPH, DTM&H
Deputy Editor
Allyson Bloom, MD


Pelvic inflammatory disease (PID) refers to acute infection of the upper genital tract structures in women, involving any or all of the uterus, oviducts, and ovaries; this is often accompanied by involvement of the neighboring pelvic organs. By definition, PID is a community-acquired infection initiated by a sexually transmitted agent, distinguishing it from pelvic infections caused by medical procedures, pregnancy, and other primary abdominal processes.

Pelvic inflammatory disease in the United States annually accounts for about 2.5 million outpatient visits, 200,000 hospitalizations, and 100,000 surgical procedures [1]. It is the most frequent gynecologic cause for emergency department visits (350,000/year) and incurs an annual total expense of almost $2 billion [1,2]. However, costs of PID in the US have decreased in the last decade [3].

The pathogenesis of and risk factors for PID will be reviewed here. The clinical features, diagnosis, treatment, and sequelae of this disorder are discussed separately. (See "Clinical features and diagnosis of pelvic inflammatory disease" and "Treatment of pelvic inflammatory disease".)


The vaginal flora of most normal, healthy women includes a variety of potentially pathogenic bacteria [4]. Among these are species of streptococci, staphylococci, Enterobacteriaceae (most commonly Klebsiella spp, Escherichia coli, and Proteus spp), and a variety of anaerobes. Compared with the dominant hydrogen peroxide-producing Lactobacillus acidophilus, these organisms are present in low numbers, and ebb and flow under the influence of hormonal changes (pregnancy, degree of estrogenization), contraceptive method, sexual activity, and other as yet unknown forces.

Complete disruption of the vaginal ecosystem can occur, in which anaerobic bacteria assume predominance over the desirable strains of lactobacilli. This condition is known as bacterial vaginosis, which is not associated with an inflammatory response [5]. Bacterial vaginosis affects 15 to 30 percent of American women, one-half of whom are asymptomatic [6]. Its significance is not clearly understood but when found in pregnancy, bacterial vaginosis was an independent risk factor for preterm delivery of a low birthweight infant in a study of 10,397 women of whom 16 percent had the diagnosis [7]. An intermediate situation in which H202-producing lactobacilli and anaerobes coexist in roughly equal numbers is called a transitional flora.


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Literature review current through: Dec 2014. | This topic last updated: Aug 17, 2012.
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