Background: Given recent increasing case rates of Chlamydia trachomatis infection, we evaluated trends in chlamydia rates and related health outcomes in women and men aged 15 to 44 years who were enrolled in a Pacific Northwest health plan.
Methods: We identified chlamydia, pelvic inflammatory disease (PID), ectopic pregnancy, and male urethritis cases occurring annually during 1997-2007 using computerized health plan databases, calculating rates per 100,000 person-years (py) by gender and 5-year age groups. We also calculated annual chlamydia testing rates.
Results: In women, chlamydia testing rates increased by approximately 23% (220 tests per 1000 py in 1997 to 270 tests per 1000 in 2007). Chlamydia diagnosis rates rose from 449 cases/100,000 py in 1997 to 806/100,000 in 2007, a 79% increase (P = 0.01). Increases were greatest during 2005-2007, also the period of major conversion to nucleic acid amplification test. PID rates in this interval declined steadily from 823 cases/100,000 py to 473/100,000 (P < 0.01). Ectopic pregnancy rates remained unchanged. In men, chlamydia testing rates increased nearly 3.5-fold, from 12 to 42 tests per 1000 py. Chlamydia rates for men also rose significantly throughout the study interval (from 91 cases/100,000 py to 218/100,000; P < 0.01) as did urethritis diagnosis rates (P < 0.01).
Conclusion: Between 1997 and 2007, annual health plan chlamydia rates increased significantly for both women and men. These trends may be due in part to increased testing rates and increased use of more sensitive tests, but they likely do not explain the increased urethritis rates. During this same interval, we observed steady declines in PID rates, consistent with other national data sources.