of infection, as well as differences in laboratory standards. In general, gonococcal PID is associated with more clinically severe symptoms than chlamydial upper genital tract infections, although the latter are more insidious.

Teenagers have a particularly high rate of PID, especially when the data are corrected for level of sexual activity (Shafer and Sweet, 1989). In the United States, for example, sexually active 15- to 19-year-old females have a one in eight estimated lifetime risk of suffering PID (Shafer and Sweet, 1989). Rates are probably higher in developing countries, given the higher prevalence of infection and more limited access to care. As described above, biological, behavioral, and social determinants raise the risk of RTIs among teenagers, so creative interventions are needed to reach this high-risk age group.

The role of atypical (also called "subclinical" or "silent") PID in causing adverse reproductive sequelae is becoming increasingly apparent (Cates and Wasserheit, 1991). Atypical salpingitis accounts for a sizable proportion of tubal infertility. Many investigations have found that more than one-half of women with documented tubal occlusion reported no history of previous PID, despite serologic evidence of past chlamydial or gonococcal infection (Cates and Wasserheit, 1991). Moreover, morphologic and physical analysis of tubal epithelium from women with distal tubal obstruction found extensive ultrastructural damage, even among women who had no knowledge of previous PID (Patton et al., 1989). Women with atypical salpingitis had levels of tubal abnormalities similar to those with overt salpingitis. No demographic or clinical determinants have been found that differentiate women with atypical salpingitis from those with symptomatic PID (Cates, Joesoef, and Goldman, 1993). Thus, clinical evidence of symptomatic PID is not a necessary precursor for the eventual development of tubal dysfunction or obstruction.

Infertility

Women with a self-reported history of PID are more likely to be infertile than those without. A WHO multicenter study of infertile couples showed the proportion of infectious causes of infertility in different parts of the world: in Africa, nearly four-fifths of couples had an infectious etiology, compared with about two-fifths of infertile couples in other developing countries and one-fifth of couples seeking infertility services in developed countries (Cates et al., 1985).

Infertility as a consequence of RTI occurs primarily through the damage caused by salpingitis, which in turn leads to tubal dysfunction and occlusion. Usually this damage involves antecedent lower genital tract infections with either N. gonorrhoeae or C. trachomatis.



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