What do diagnoses of pelvic inflammatory disease in specialist sexual health services in England tell us about chlamydia control?

Background. Pelvic inflammatory disease (PID) is an outcome measure for the evaluation of chlamydia screening programmes. We explore PID diagnoses in specialist sexual health services (SSHS) in England to inform the evaluation of the national chlamydia screening programme (NCSP), which was implemented nationally in 2008.

Methods. We conducted descriptive analyses using data on diagnoses of PID- with and without chlamydia (CT) and/or gonorrhoea (GC)- by age and year of birth, in SSHS between 2009 and 2019 from the GUMCAD database. Rates were calculated per 100,000 females residing in England.

Results. CT screening activity peaked in 2010. The rates of all PID diagnoses decreased between 2009-2019 by 39%. CT-associated PID (CT-PID) declined by 58%, and non-specific PID declined by 37%. GC37 PID increased by 34%. CT-PID decreased across all age groups with the highest observed decline, 71%, in 15 to 19-year olds. A dose response relationship was observed between CT-PID rates and screening, with rates lowest in those with the greatest exposure to screening.

Discussion. There was a marked decline in diagnoses of CT-PID, and non-specific PID, at SSHS after the introduction of wide-spread chlamydia screening, whilst GC-PID diagnoses increased. This ecological trend was broadly consistent with what we would have expected to see if widespread screening reduced the incidence of chlamydia-associated PID (and of non-specific PID), as has been observed in randomised controlled trails of screening.