Pelvic inflammatory disease (PID) is a clinical syndrome comprising a spectrum of infectious and inflammatory diseases of the upper female genital tract. The diagnosis of pelvic inflammatory disease (PID) can include any combination of endometritis, salpingitis, tubo-ovarian abscess, or pelvic peritonitis. Each of these disease processes is characterized by ascending spread of organisms from the vagina or cervix to the structures of the upper female genital tract. Although PID is most notable for the associated risk of severe, long-term sequelae, the infections may be asymptomatic ("silent") or overt with mild to severe symptoms. The clinical syndrome of acute (and subacute) PID—usually defined as symptoms for fewer than 30 days—can be due to a variety of pathogens, often including, but not limited to, Neisseria gonorrhoeae and Chlamydia trachomatis. In contrast, chronic pelvic inflammatory disease (symptoms for greater than 30 days) is a separate disorder usually related to infection by Mycobacterium tuberculosis or Actinomyces species . This module will focus on acute and subacute PID.
There is no single diagnostic test for PID and in the United States PID is not a nationally notifiable disease; thus, it can be difficult to accurately estimate the incidence of PID. Review of a national admission database in 2001 estimated more than 750,000 cases of PID occurred in the United States. More recent data from the National Health and Nutrition Examination Survey (NHANES) 2013–2014 estimated a prevalence of self-reported lifetime PID of 4.4% among sexually experienced women 18-44 years of age, which corresponds with an estimate of 2.5 million women aged 18-44 ever having PID in their lifetime. Available data point to an overall trend of decline in the incidence of PID in the United States. A review of national insurance claims found a 25.5% decline in cases from 2001 to 2005 (317.0 to 236.0 per 100,000 enrollees). The number of initial visits to office-based physicians for PID declined by 71% between 2005 and 2014—from 176,000 visits in 2005 to 51,000 visits in 2014 (Figure 1). Data from 1995 through 2013 likewise show a consistent decrease in the lifetime prevalence of treatment for PID and these decreases occurred across multiple racial/ethnic groups (Figure 2).[6,7]
The trend of decreasing PID is primarily attributed to an increase in effective screening and treatment of chlamydial and gonococcal infections in adolescents and young women.[8,9] Although total rates of infection with C. trachomatis have increased in some populations, the rates of PID have consistently fallen. This highlights the effectiveness of treating lower tract chlamydial infections for prevention of progression to upper tract disease. Of note, several studies suggest a decrease in the proportion of cases attributable to chlamydial infection. As pathogens other than C. trachomatis and N. gonorrhoeae are becoming more prominent as a cause of PID, the importance of addressing risk behaviors and monitoring for infections caused by these other organisms may become more important.
Despite a decline in the incidence of PID, the cost of treatment remains significant. An analysis performed in 2008 estimated an average direct medical cost of $3,202 per case of PID. In 2000, investigators from the CDC reported their findings estimating direct medical expenditures for PID and three major sequelae (chronic pelvic pain, ectopic pregnancy, and infertility); the estimated overall cost in 1998 for PID was $1.88 billion, including $1.06 billion for inpatient and outpatient direct treatment of PID, $166 million for chronic pelvic pain, $295 million for ectopic pregnancy, and $360 million for infertility associated with PID. These costs have likely decreased somewhat as the incidence of PID has fallen since 2005.
Epidemiologic studies have revealed numerous risk factors associated with pelvic inflammatory disease and many of these risk factors overlap with those known to be associated with acquisition of infections that cause PID. Multiple partners, age younger than 20 years, and current or prior infection with gonorrhea or chlamydia have consistently been demonstrated as significant risk factors. Other possible risk factors include history of PID, male partners with gonorrhea or chlamydia, current douching, insertion of IUD, bacterial vaginosis, and oral contraceptive use.[7,14] The following provides more detail on the major risk factors:
- Age and Age of Sexual Debut: Several studies have identified age less than 20 years as a major risk factor for the development of PID.[13,15] The increased risk of PID in younger women correlates with the high rates of chlamydia and gonorrhea infection in female adolescents and young adult women. In addition, cervical ectopy—the composition of the cervical epithelium that is often present in adolescents—allows for more efficient access of infectious pathogens to the vulnerable target cells. Younger sexual debut is also a risk factor for PID. In the NHANES 2013-2014, the lifetime PID prevalence in sexually experienced women aged 18-44 years was higher than in those with a younger sexual debut (Figure 3).
- Number of Sexual Partners: Several studies have shown a correlation with greater number of sexual partners and risk of PID. Most recently, in NHANES 2013-2014, the lifetime PID prevalence was approximately three times greater in women with 10 or more lifetime vaginal sex partners than in women with one partner (Figure 4).
- History of PID: A prior history of PID increases the risk for developing PID. The damage that occurs to the fallopian tube mucosa during an episode of PID makes women more susceptible to recurrent infection. Having a history of a gonorrheal or chlamydial infection increases the likelihood of recurrent disease, which, in turn, increases the risk for PID. A woman’s risk also increases if her male partner has gonorrhea or chlamydia.
- Vaginal Douching: Douching is thought to increase the risk for PID because it contributes to vaginal flora changes, epithelial damage, and disruption of the cervical mucous barrier, all of which can increase the likelihood of developing PID.[7,14] The relationship between douching has been called into question in more recent studies and the recommendation for or against vaginal douching is currently subject to debate. The relationship of bacterial vaginosis (BV) to PID is similarly unclear. Although the anaerobic bacteria associated with BV have been detected in the upper genital tract in association with PID, epidemiologic analyses have not consistently shown a clear association between BV and development of PID.
- Intrauterine Device (IUD): The insertion of an intrauterine device (IUD) has been shown to increase the risk of PID approximately six-fold within the first 21 days of placement, but after 21 days, the risk returns to baseline. In addition, the CDC describes mucopurulent cervicitis or current N. gonorrhoeae and/or C. trachomatis infection as “unacceptable health risk” and thus a contraindication to IUD insertion. Notably, recent studies have revealed that the rates of PID among new IUD users were 1% or below for both those who tested positive for N. gonorrhoeae and/or C. trachomatis and those who tested negative.[20,21] The authors of these recent studies suggest that women without clinical evidence of active infection can have intrauterine system placement and sexually transmitted infection screening, if indicated, on the same day. This remains an active area of investigation.
- Oral Contraceptive Use: Oral contraceptive (OC) use may increase the risk of cervical chlamydial infection due to cervical ectopy associated with OC use. OC use also causes thickening of the cervical mucous, which may be protective against lower genital tract organisms ascending into the upper genital tract. Overall, many providers conclude that since the absolute risk of pelvic infection is small (1.6 cases per 1,000 woman-years in a meta-analysis) the benefits of these birth-control measures likely outweigh the risks.