Incident cases available for the study
The incidence of first episode of PID seen in general practice fell during the study period, from 19.3/10 000 person-years in 2003 to 8.9/10 000 person-years in 2007. The incidence rate was highest in women aged 20–24 years, and rose from 28.4 to 30.4/10 000 person-years between 2003 and 2004 but then fell to 14.2/10 000 person-years in 2007. Incidence in all other age-groups fell progressively from 2003 to 2007, with the greatest decline in younger age groups (P = 0.04 for interaction in Poisson models).