Increasing Chlamydia Positivity in Women Screened in Family
Planning Clinics: Do We Know Why?
DAVID FINE, PHD,* LINDA DICKER, PHD,† DEBRA MOSURE, PHD,† STUART BERMAN, MD,† AND REGION X
INFERTILITY PREVENTION PROJECT
increased 46% from 1997 through 2004 among young sexually active
women screened in Region X family planning clinics. The objective of
this analysis was to systematically examine the influences of risk
factors, changing laboratory test methods, and interclinic variability
on chlamydia positivity during this period.
We analyzed data from 520,512 chlamydia tests
from women aged 15 to 24 years screened in 125 family planning
clinics. Multivariate logistic regression modeling was used to adjust the
annual risk of chlamydia for the demographic, clinical, and sexual risk
behavior characteristics associated with infection and for the increas-
ing use of more sensitive laboratory test methods. A generalized linear
mixed model was used to adjust for interclinic variability.
Results: We found a significant 5% annual increase in the risk of
chlamydia even after adjusting for risk factors including laboratory
test characteristics (odds ratio 1.05, 95% confidence interval: 1.04,
1.06). Variability among the clinics where screening occurred did not
account for the increase.
Conclusions: Based on a review of all available data, we concluded
that there was a true increase in chlamydia positivity over the 8-year
Following a 9-year 60% decline, chlamydia positivity
CHLAMYDIA TRACHOMATIS IS THE MOST common bacterial
sexually transmitted infection (STI) in the United States, with an
estimated 2.8 million new cases occurring each year.1Chlamydial
infections are often asymptomatic, can persist for a prolonged
period, and are an important preventable cause of reproductive
sequelae in women, including pelvic inflammatory disease (PID),
ectopic pregnancy, and infertility.2Screening for chlamydia has
been shown to reduce the incidence of PID.3
In 1988, the first widespread screening and treatment program
for chlamydia began in US Public Health Service Region X
(Alaska, Idaho, Oregon, and Washington). The focus of the Region
X Infertility Prevention Project is to screen all young sexually
active women seen in the region’s Title X family planning clinics.4
During the first 9 years of the program, chlamydia positivity
among women aged 15 to 24 years declined over 60%, from 10.3%
in 1988 to 4.0% in 1996.5This decline corresponded with signif-
icant reductions in self-reported sexual risk behaviors.6Similar
declines in chlamydia positivity were also seen in other areas of
the United States where broad-based screening programs were
instituted during the same time period.7–9However, there was a
46% increase in chlamydia positivity, from 3.9% in 1997 to 5.7%
in 2004, among young women screened in Region X family planning
clinics.5There have been many questions and much speculation about
the reasons for the increases in positivity, including changes in labo-
ratory test technology and screening higher-risk women; however,
there have been no analyses systematically evaluating potential
causes for these increases. The 3 objectives of our analysis were to
examine: 1) demographic, clinical, and sexual behavioral risk
characteristics associated with chlamydial infection and their in-
fluences on chlamydia positivity in women aged 15 to 24 years
seen in Region X family planning clinics from 1997 through 2004;
2) the impact of changing laboratory test methods on the increases
in positivity; and 3) the effect of interclinic variability on chla-
mydia positivity using a generalized linear mixed model.
Materials and Methods
We analyzed data from 520,512 chlamydia tests from women aged
15 to 24 years screened in 125 family planning clinics participating in
the Region X Infertility Prevention Project from 1997 through 2004
(average 65,000 tests/yr). Women aged 24 years and younger were
routinely screened for chlamydial infection at least annually as rec-
ommended by the Centers for Disease Control and Prevention and the
US Preventive Service Task Force.10,11
All Region X family planning clinics used a common medical
record form. Information collected included age; race; ethnicity;
specimen collection date; clinical findings (ectopy, friable cervix,
PID, cervicitis); self-reported sexual risk behaviors (having had a
new sex partner in the past 60 days, having had multiple sex
partners in the past 60 days, having had a symptomatic sex partner
in the past 60 days, having had a sex partner who was diagnosed
with chlamydia, and condom use during last sex); having had
chlamydia in the past year; laboratory test type; and chlamydia test
result. We included clinics that routinely screened for chlamydia
during the entire 8-year period and had performed 50 or more
chlamydia tests in at least 7 of the 8 years (about 90% of all
chlamydia tests performed). We used data from the US Census to
Supported by Region X IPP, HHS/OPA and CDC/DSTDP.
Use of trade names and commercial sources is for identification only
and does not imply endorsement by the Centers for Disease Control and
Correspondence: David Fine, PhD, Center for Health Training, 1809
Seventh Avenue, Suite 400, Seattle, WA 98101-1313. E-mail: dfine@jba-
Received for publication March 16, 2007, and accepted June 12, 2007.
From the *Center for Health Training, Seattle, Washington;
and †Division of Sexually Transmitted Disease Prevention, Centers
for Disease Control and Prevention, Atlanta, Georgia
Sexually Transmitted Diseases, November 2007, Vol. 34, No. 11, p.000–000
Copyright © 2007, American Sexually Transmitted Diseases Association
All rights reserved.
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Sexually Transmitted Diseases ● November 2007
FINE ET AL