Table 3.

 Incidence of pelvic inflammatory disease (PID) in 2377 women followed up for 12 months. Values are percentages (numbers) unless stated otherwise

Variables	Screened women	Deferred screening controls	Relative risk (95% CI)	P value
All PID: probable* and possible†	1.3 (15/1191)	1.9 (23/1186)	0.65 (0.34 to 1.22)	0.19
Probable PID	0.8 (10/1191)	1.3 (16/1186)	0.62 (0.29 to 1.34)	0.24
Rate of PID in women who were positive for chlamydia at baseline	1.6 (1/63)	9.5 (7/74)	0.17 (0.03 to 1.01)	0.07

*Doctor assessed as probable—that is, clinical diagnosis of PID and treated¹; modified Hager’s criteria—pelvic pain, cervical motion tenderness, uterine or adnexal tenderness.¹⁸

†Abdominal pelvic pain with features of PID, which may have responded to antimicrobial therapy, but no record of cervical excitation or uterine or adnexal tenderness; or long standing abdominal pain consistent with endometriosis, but some features of PID—for example, uterine tenderness, and unable to confirm if antimicrobial therapy had a benefit.¹