Chlamydia Positivity and Cost per Case Detected in Asymptomatic Women over 25 Years in an STD Clinic

Background: CDC currently recommends against routine chlamydia screening of asymptomatic women >25 years, but recommends screening high-risk older women.  What constitutes high-risk remains undefined and the program costs associated with screening these women remains unknown.  We sought to determine 1) chlamydia positivity among asymptomatic tested women >25; and, 2) costs associated with detecting chlamydial cases in this population.

Methods: We retrospectively analyzed Public Health – Seattle & King County STD Clinic data from January 1, 2004 – October 25, 2013 to describe the population of asymptomatic women, excluding those with known contact to chlamydia or gonorrhea, tested for genital chlamydia infection.  We sought to identify factors associated with test positivity and calculate the laboratory testing costs per case detected. 

Results: During the study period, 8,261 asymptomatic women >25 attended the clinic for new problem visits; this group represented 31% of all female visits, and 55% of these women sought care for routine STD screening.  5,320 women underwent chlamydial testing, and 104 tested positive (1.95%).  Test positivity was highest among Hispanics (4.4% of 181 tested), Asians (3.9% of 409 tested), Native American/Alaskan Natives (3.8% of 131 tested), and women aged 26-30 (3.24% of 2,100 tested).  Test positivity did not vary significantly by number of sexual partners, drug use, or history of chlamydia or another bacterial STD in the last 12 months.  The laboratory cost per case detected was $1,254.73, with an overall cost for chlamydia testing of $140,530 over 10 years.

Conclusions: Overall, chlamydia positivity among asymptomatic women >25 at our STD Clinic is low. At the same time, eliminating the laboratory cost of chlamydia testing in this group would save relatively little money.  In an era of near-universal healthcare, shifting the care of this low-risk population to primary care clinics could save additional costs while focusing STD Clinic resources on higher-risk populations.