Heterogeneity in risk of pelvic inflammatory diseases after chlamydia infection: a population-based study in Manitoba, Canada.
BACKGROUND
The association between chlamydia infection and pelvic inflammatory disease (PID) is a key parameter for models evaluating the impact of chlamydia control programs. We quantified this association using a retrospective population-based cohort.


METHODS
We used administrative health data sets to construct a retrospective population-based cohort of women and girls aged 12-24 years who were resident in Manitoba, Canada, between 1992 and 1996. We performed survival analysis on a subcohort of individuals who were tested for chlamydia to estimate the risk of PID diagnosed in a primary care, outpatient, or inpatient setting after ≥ 1 positive chlamydia test.


RESULTS
A total of 73 883 individuals contributed 625 621 person years of follow-up. Those with a diagnosis of chlamydia had an increased risk of PID over their reproductive lifetime compared with those who tested negative (adjusted hazard ratio [AHR], 1.55; 95% confidence interval [CI], 1.43-1.70). This risk increased with each subsequent infection: the AHR was 1.17 for first reinfection (95% CI, 1.06-1.30) and 1.35 for the second (95% CI, 1.04-1.75). The increased risk of PID from reinfection was highest in younger individuals (AHR, 4.55 (95% CI, 3.59-5.78) in individuals aged 12-15 years at the time of their second reinfection, compared with individuals older than 30 years).


CONCLUSIONS
There is heterogeneity in the risk of PID after a chlamydia infection. Describing the progression to PID in mathematical models as an average rate may be an oversimplification; more accurate estimates of the cost-effectiveness of screening may be obtained by using an individual-based measure of risk. Health inequalities may be reduced by targeting health promotion interventions at sexually active girls younger than 16 years and those with a history of chlamydia.
Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London.
Bethan
B
Davies
Department of Infectious Disease Epidemiology, School of Public Health, Imperial College London.
Helen
H
Ward
Centre for Global Public Health, Department of Community Health Sciences, University of Manitoba.
Stella
S
Leung
School of Social and Community Medicine and School of Clinical Veterinary Science, University of Bristol, United Kingdom.
Katy M E
KM
Turner
Bill and Melinda Gates Foundation, Seattle, Washington.
Geoff P
GP
Garnett
Centre for Global Public Health, Department of Community Health Sciences, University of Manitoba.
James F
JF
Blanchard
Centre for Global Public Health, Department of Community Health Sciences, University of Manitoba Public Health Branch, Manitoba Health, Winnipeg, Canada.
B Nancy
BN
Yu
D000293:Adolescent; D000328:Adult; D017677:Age Distribution; D000367:Age Factors; D002648:Child; D002690:Chlamydia Infections / Q000150:complications* / Q000453:epidemiology; D002692:Chlamydia trachomatis; D005260:Female; D006801:Humans; D053208:Kaplan-Meier Estimate; D008350:Manitoba / Q000453:epidemiology; D000292:Pelvic Inflammatory Disease / Q000453:epidemiology / Q000382:microbiology*; D016016:Proportional Hazards Models; D012189:Retrospective Studies; D012306:Risk; D055815:Young Adult
Chlamydia trachomatis; cohort study; cost effectiveness; epidemiology; mathematical models; pelvic inflammatory disease; retrospective study