Chlamydia Positivity in American Indian/Alaska Native Women
Screened in Family Planning Clinics, 1997–2004
LINDA GORGOS, MD, MSC,* DAVID FINE, PHD,† AND JEANNE MARRAZZO, MD, MPH*
mydia trachomatis (CT) infections within American Indian/Alaskan
Native (AI/AN) populations but there are few analyses of CT preva-
lence in these populations over time.
Methods: We analyzed data from 7374 visits at which diagnostic
tests for CT were collected in AI/AN women aged 15 to 24 years seen
at family planning clinics associated with the Region X Infertility
Prevention Project. Trends in population characteristics and test pos-
itivity were examined and compared with non-AI/AN women tested in
the same setting and time period. Chlamydia positivity was adjusted
for changes in diagnostic test type. Multivariable logistic regression
was used to identify characteristics associated with infection.
Results: Adjusted CT positivity in AI/AN women rose from 7.8%
to 11.0%, which was 1.5 to 2.2 times the non-AI/AN population levels
over the study period (absolute difference 2.8%–6.6%). Differences
persisted after correction for test type and age. Temporal changes in
positivity among AI/AN women were associated with a rise in reported
risk behaviors and decline in age of the population being tested. Risk
factors associated with positivity among AI/AN women were younger
age, >1 behavioral risks, >1 clinical findings, partner with chlamydia,
chlamydia in past year, and pregnancy related visit.
Conclusions: AI/AN women had consistently higher levels of chla-
mydia positivity than non-Native women, even after adjustment for
age and diagnostic test. Further investigation of risks for chlamydia,
related outcomes, access to screening, sexual networks, and enhanced
surveillance would be beneficial for improving health in this vulnera-
Previous studies demonstrated high levels of Chla-
CHLAMYDIA TRACHOMATIS (CT) INFECTIONS ACCOUNT
for the largest proportion of sexually transmitted infections re-
ported to the Centers for Disease Control and Prevention (CDC),
with an estimated 2.8 million new cases per year in the United
States.1American Indians/Alaskan Natives (AI/AN) represent a
racial minority population within the United States with a unique
social, cultural, and biologic background. AI/AN bear a dispro-
portionate burden of illness for many diseases, including sexually
A high prevalence of chlamydial infection has been reported in
AI/AN communities, ranging from 24% to 30% among prenatal
patients in the Southwest5,6to 23% of all women screened in a
remote Alaskan village.7In 2004, women aged 15 to 44 years
screened for chlamydia in 2 Indian Health Service (IHS) regions
had chlamydia positivities of 10.7% versus 6.3% for women
screened in family planning clinics nationwide.8In a recent report,
the overall chlamydia rate in 2004 among AI/AN residing in IHS
provision areas was 2.3 times higher than the corresponding US
rates, with 3 IHS areas having chlamydia rates 4.9 to 6 times
higher than the US rate.3However, there are few analyses of
chlamydia infections over time in AI/AN populations.
We sought to more clearly define the clinical epidemiology and
trends in test positivity of chlamydial infections in AI/AN women
by examining data representing 15- to 24-year-old AI/AN women
attending family planning clinics in the Region X Infertility Pre-
vention Project (IPP) network during the years 1997–2004. This
represents a cohort of women for whom universal screening for
chlamydia was recommended throughout the study period.9,10
Materials and Methods
Sources of Data
Data on chlamydia tests were obtained from the Region X IPP,
an ongoing program since 1988 that provides for the screening and
treatment of chlamydial infections throughout Alaska, Idaho, Or-
egon, and Washington states. All women aged 15 to 24 years who
presented to family planning clinics enrolled in the IPP and who
self-identified as AI/AN, whether as a sole racial category or in
combination with another racial or ethnic category, were included
in this analysis. Since inception of the IPP in 1988, screening has
been recommended for all women aged 24 years and younger for
chlamydial infection at least annually as recommended by the
CDC and the US Preventive Services Task Force.10,11
All Region X family planning clinics used a common medical
record form and laboratory slip to record a standard set of infor-
mation. Information collected included age, race, ethnicity, spec-
imen collection date, reason for visit, specified clinical exam
findings (ectopy, friable cervix, pelvic inflammatory disease, cer-
vicitis), self-reported sexual risk behaviors (having had a new sex
partner in the past 60 days, multiple sex partners in the past 60
days, a symptomatic sex partner in the past 60 days, 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. CT diagnostic tests with unsatisfactory
or indeterminate results were excluded from the analysis.
Supported by US Public Health Service Training Grant AI-07140 (to
L.G.); Region X Infertility Prevention Project.
Correspondence: Linda Gorgos, MD, MSc, Harborview Medical Center,
Center for AIDS and STD, Mailbox 359931, 325 Ninth Avenue, Seattle,
WA 98104. E-mail: firstname.lastname@example.org.
Received for publication November 19, 2007, and accepted February 11,
From the *Division of Allergy and Infectious Diseases, University of
Washington; and †Center for Health Training, Seattle, Washington
Sexually Transmitted Diseases, December 2008, Vol. 35, No. 12, p.000–000
Copyright © 2008, American Sexually Transmitted Diseases Association
All rights reserved.
CT testing for the family planning clinics was performed by 4
state public health laboratories (Alaska, Idaho, Oregon, and Wash-
ington), a county health district laboratory (Spokane), and the
University of Washington Chlamydia Laboratory. From 1997
through 2004, these laboratories adopted nucleic acid amplification
tests (NAATs) in favor of less sensitive assays. During the study
period, non-NAATs included (in order of decreasing usage) en-
zyme immunoassay (MicroTrak II, Syva and Behring Diagnostic
Products, Cupertino, CA); nucleic acid hybridization test (Pace 2,
Gen-Probe, San Diego, CA); nucleic acid hybridization assays
(Hybrid Capture 2, Digene, Gaithersburg, MD) and cell culture.
The majority of NAATs used in Region X were ligase chain
reaction tests (LCx, Abbott, Abbott Park, IL) and target capture
transcription-mediated amplification assays (Aptima Combo 2,
Gen-Probe, San Diego, CA).12
Chlamydia positivity was calculated by dividing the number of
positive tests by the total number of tests performed. Categorical
variables were analyzed with the method of chi-squared, with time
trends in demographic variables examined for both heterogeneity
and trend. Potential predictors of chlamydia positivity were iden-
tified by univariate analysis of odds ratios. Stepwise forward
logistic regression modeling was used to identify factors indepen-
dently associated with chlamydia positivity, including demo-
graphic characteristics, clinical findings, self-reported sexual risk
behaviors, type of laboratory test (NAAT vs. non-NAAT), and
year of test. In comparing observed chlamydia positivity in AI/AN
versus non-AI/AN women in Region X, direct standardization was
used to correct for age differences between the 2 populations. All
values are reported at the 95% confidence interval.
As conversion to a more sensitive laboratory test can result in an
increase in observed chlamydia positivity even with no increase in
true disease prevalence,13,14we adjusted for change in test type
used over time. We used the sensitivity and specificity of each
laboratory test method to calculate an adjusted positivity [test-
specific adjusted positivity ? (test-specific observed positivity ?
test specificity ? 1)/(test sensitivity ? test specificity ? 1)].15
Overall adjusted positivity was calculated as a weighted sum of the
adjusted positivity for each test type. This method has previously
been used in reporting of chlamydia positivity data by the CDC as
detailed by Fine and Dicker et al.8,12,13The sensitivity and spec-
ificity estimates used for the adjustment were culture (sensitivity
0.747, specificity 1.000); enzyme immunoassay tests with negative
gray zone confirmation (sensitivity 0.810, specificity 0.996); other
non-NAATs including Gen-Probe Pace 2 and Digene Hybrid Cap-
ture 2 assay (sensitivity 0.619, specificity 0.997); and NAATs
(sensitivity 0.855, specificity 0.997).16,17We compared the differ-
ences in trends for observed and adjusted chlamydia positivity.
From 1997 to 2004, a total of 581,106 CT tests were performed,
with 7449 tests performed in AI/AN women. Of the 7449 chla-
mydia tests performed among women who self-reported as AI/AN,
75 (1.0%) had unsatisfactory, indeterminate, or missing results and
were excluded from further analysis. Of the remaining 7374 chla-
mydia tests, 67% were done in Washington state, 18% in Oregon,
10% in Alaska, and 5% in Idaho. By racial/ethnic categories, 90%
of women tested reported being AI/AN alone, 8% reported AI/AN
race with Hispanic ethnicity, and 2% reported more than 2 racial/
ethnic categories. Nearly all chlamydia tests performed on both
AI/AN and non-AI/AN women were based on cervical specimens
(91.4% and 94.5%, respectively) with urine specimens being the
next most common specimen site (8.4% and 5.4%, respectively).
The use of NAAT-based test methods increased rapidly beginning
in 1997. During the study period, the use of NAAT-based tests
rose from 13% to 60% in the region at large and from 13% to 78%
among AI/AN women. From 1997 to 2004, other test methods
used among AI/AN women changed as follows: enzyme immu-
noassay (46%–0%), culture (27%–0.8%), and non-NAAT nucleic
acid hybridization (14%–22%).
Among AI/AN women, those aged 15 to 17 accounted for
30.4% of tests, aged 18 to 19 for 25.8%, and aged 20 to 24 for
43.8% of tests (Table 1). Most women (70.2%) presented for a
“routine visit” (initial or annual gynecologic exam, primary care
visit, reproductive health exam). Thirteen percent of women had a
“pregnancy related” visit, defined as request of a pregnancy test,
prenatal care, pregnancy management, or pre/postabortion ser-
vices, and 16.1% reported the reason for visit as having symptoms
(abnormal vaginal or urethral discharge, dysuria, abdominal or
pelvic pain, or abnormal vaginal bleeding). Overall, 33.3% of
women reported 1 or more behavioral risk factors in the 60 days
before testing, including 28.9% with a new partner, 14.5% with
more than 1 sex partner, and 3.1% with a symptomatic sex partner.
Condom use at last sexual encounter was low at 27.3%. Few
women (8.8%) had clinical findings on examination. Seven percent
of women reported having a chlamydial infection in the 12 months
before the most recent test.
Through the study period, the age structure and risk profile of
the AI/AN women aged 15 to 24 being tested at IPP family
planning clinics demonstrated considerable variation (Fig. 1). The
proportion of women aged 15 to 17 rose from 33.5% in 1997 to a
peak of 35.6% in 2000 and then fell to 26.1% in 2004
(P ?0.0001). There was a similar rise in reported sexual risk
behaviors over this period, with women reporting one or more risk
factors of new sexual partner, multiple partners, or symptomatic
partner rising from 26.8% in 1997 to a peak of 35.4% in 2000 and
then falling to 25.7% in 2004 (P ?0.0001). Reported condom use
did not vary over time. Toward the end of the study period, more
women reported being diagnosed with chlamydia in the past 12
months, rising from 3.9% in 1997 to 8.3% in 2004 (P ? 0.002).
Compared with women aged 15 to 24 tested at family planning
in Region X from 1997 to 2004 who reported non-AI/AN race,
there were differences in age and risk profiles. AI/AN women were
younger: proportion aged 15 to 17 years, 30.4% versus 22.8%
(P ?0.0001); aged 18 to 19, 25.8% versus 26.5% (P ? 0.21); and
age 20 to 24, 43.8% versus 50.7% (P ?0.0001). AI/AN women
were more likely to report having genitourinary symptoms at the
time of visit (16.1% vs. 13.2%, P ?0.001) and were more likely to
present for a pregnancy related visit (13.1% vs. 8.1%, P ?0.001)
than non-AI/AN women. Sexual behavioral risks in the 60 days
before testing were more commonly reported among AI/AN wom-
en: new sex partner, 28.9% versus 22.9% (P ?0.0001); multiple
sex partners, 14.5% versus 9.7% (P ?0.0001); symptomatic sex
partner, 3.1% versus 2.4% (P ? 0.0004); and 1 or more behavioral
risks, 33.3% versus 25.6% (P ?0.0001). Reported condom use at
last sex was low in both groups, 27.3% for AI/AN women versus
25.8% (P ? 0.007). Notably, AI/AN women were more likely to
have been diagnosed with chlamydia in the past 12 months, 7.2%
versus 3.9% (P ?0.0001).
Observed, unadjusted chlamydia positivity for AI/AN women
was 8.6% versus 5.2% in the non-AI/AN population. After direct
standardization was used to correct for age differences between the
AI/AN population and the Region X non-AI/AN population, ob-
served positivity changed minimally (8.6%–8.4%).
Sexually Transmitted Diseases ● December 2008
GORGOS ET AL.
Trends in chlamydia positivity over time, adjusted for test type,
are displayed in Figure 2. Adjusted positivity in AI/AN women
rose from 7.8% in 1997 to a peak of 12.1% in 1999, concluding at
11.0% in 2004. These changes in positivity were temporally asso-
ciated with a rise in reported risk behaviors and a decline in the age
of the population being tested. Adjusted chlamydia positivity in
non-AI/AN women rose steadily from 4.6% in 1997 to 7.1% in
2004. Comparing test type adjusted positivity by calendar year,
AI/AN women had chlamydia positivity ranging from 1.5 to 2.2
times the non-AI/AN population levels (absolute difference 2.8%–
6.6%). At all time points, chlamydia positivity in AI/AN women
was higher than that reported in both the non-AI/AN and Region
Table 2 displays risk factors independently associated with
chlamydia positivity among AI/AN women as determined by
multivariable logistic regression. Despite the observation that use
of NAAT was associated with increased positivity, as expected,
several other risks were independently associated with positivity.
These included younger age (?20 years), report of one or more
behavioral risk factors, presence of one or more clinical findings,
report of diagnosis of chlamydia in the past 12 months or of a
partner with chlamydia, and presentation for pregnancy related
visit. After accounting for each of these factors, there was no
independent association of year of visit with chlamydia positivity.
Additionally, there was no independent association of positivity
with condom use, symptoms at the time of visit, or having a
partner with gonorrhea.
In comparison to the non-AI/AN population of women being
tested for chlamydia infection at Region X IPP family planning
clinics, AI/AN women were younger and reported higher levels of
behavioral risk factors. AI/AN women had levels of chlamydia
positivity ranging from 7.8% to 12.1% during the study period,
which was 1.5 to 2.2 times higher than positivity in the non-AI/AN
population. These differences persisted even after adjusting for age
differentials between the 2 populations.
Factors associated with chlamydia positivity in AI/AN women,
including age, test type used, behavioral risks, clinical findings,
exposure to chlamydia, and a prior positive test, were similar in
type and magnitude to other analyses of Region X data.12Of note,
a visit related to pregnancy (seeking pregnancy services or preg-
nancy testing) was associated with chlamydia positivity in this
population. A recent survey in South Carolina, part of the Region
IV IPP network, found that women aged 15 to 25 years presenting
to family planning clinics for pregnancy testing alone had a chla-
mydia positivity of 15%.18These findings emphasize that chla-
mydia testing should be performed in the population of 15- to
24-year-old AI/AN women seeking pregnancy testing or preg-
Women Aged 15 to 24 Years and C. trachomatis Positivity in
Region X Family Planning Clinics, 1997–2004
Characteristics of American Indian/Alaska Native
Age group (yrs)
Reason for visit
New sex partner, past 60 d
More than 1 sex partner,
past 60 d
Symptomatic sex partner,
past 60 d
One or more behavioral risks,
past 60 d*
Condom use last sex
Sex partner with chlamydia
One or more clinical findings†
Positive chlamydia test,
past 12 mo
*Includes having had a new sex partner, multiple sex partners, or
symptomatic sex partner in the past 60 days.
†Includes mucopurulent cervicitis, friable cervix, ectopy, and pelvic
inflammatory disease (PID).
Fig. 1. Trends in characteristics of American Indian/Alaska Native
women aged 15 to 24 years screened for chlamydia, Region X
family planning clinics, 1997–2004. Gray bar, C. trachomatis last 12
mos; ●, symptomatic partner; Œ, multiple partners; ?, new partner;
?, age 15 to 17.
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CT INFECTIONS IN AI/AN POPULATION
Our analysis is subject to several limitations. First, these data do
not necessarily reflect chlamydia positivity for all AI/AN women.
AI/AN communities are diverse geographically, socially, and cul-
turally. Importantly, our data do not account for areas within tribal
reservation lands, which may have unique issues related to sexual
networks and access to screening. A recent report from the CDC
highlighted differential chlamydia positivity between aggregate
United States data and data arising from counties predominantly
served by the IHS. Chlamydia rates in these IHS areas were 2.3
times the national average, with 11 of 12 IHS service areas having
rates higher than the US average.3
Second, the IPP program collects data on a limited number of
risk factors. AI/AN persons may have as yet unidentified protec-
tive factors or risk factors for chlamydial infection. Identifying
these factors would be valuable for future prevention and screen-
ing programs. Assessment of the influence of substance use, sexual
networks, and availability of partner treatment services in this
population should be considered.
Third, we do not have data on the extent of coverage of chla-
mydia screening for AI/AN women, although previous reports
have estimated screening coverage at 50% to 60% in Region X in
general.19,20The combined influences of area of residence, urban
versus rural versus geographically isolated, and clinic participation
in the IPP on screening coverage for AI/AN women is unknown.
Multiple previous studies have disclosed high levels of racial
misclassification among AI/AN in public health surveillance sys-
tems, including cancer registries, death certificate recording, and
reporting of HIV/AIDS and STDs.21–30Studies of mandatory, state
level sexually transmitted disease reporting in both Washington
and Oregon in 1995–2000 disclosed that 36% and 55%, respec-
tively, of reported STD cases among AI/AN were misclassified.
After adjusting for racial misclassification, case ascertainment
among AI/AN rose by 29% in Washington and by 76% in Ore-
gon.25,28The data collection protocol used in our study is designed
such that clients self-report their racial and ethnic background,
hopefully minimizing racial misclassification at the provider level.
We did not have the ability to link individual or composite visit
data to existing registries of AI/AN populations to aid in verifying
the accuracy of the racial reporting in this study.
Additionally, the population being screened over time may be
changing. Of note, our analysis demonstrated an increase in
women who reported a history of chlamydial infection in the past
12 months. This observation may reflect a true rise in background
positivity, a higher-risk group being screened, changes in clinic
practice encouraging rescreening, or an increase in the number of
women presenting for rescreening following a prior chlamydia
diagnosis as now recommended by the CDC.10
Finally, our data are not linked to individual identifiers; thus, we
cannot distinguish between women being screened repeatedly
within a defined time period. Chlamydia positivity is an estimate of
prevalence, but does not represent true prevalence in the popula-
tion. Positivity may include women who are tested 2 or more times
during a single time period. Previous comparisons of positivity
versus prevalence in family planning clinics within the IPP, in-
cluding Region X, have shown only small differences between
positivity and prevalence. In that analysis positivity was similar to
or slightly higher than prevalence with an absolute difference of
less than 0.5%. Within Region X from 1988 to 1996, on average,
93.8% of women had only 1 chlamydia test per year.31Similar data
are not available for the time period of this study for direct
Fig. 2. Trends in unadjusted and test type ad-
justed chlamydia positivity in American Indian/
Alaska Native women aged 15 to 24 years, com-
pared with adjusted chlamydia positivity in non-
AI/AN women, Region X family planning clinics,
1997–2004. ●, non-AI/AN adjusted; Œ, AI/AN unad-
justed; ?, AI/AN adjusted.
American Indian/Alaska Native Women Aged 15 to 24 Years Seen
in Region X Family Planning Clinics, 1997–2004
Adjusted Risks of Infection With C. trachomatis in
Characteristic Odds Ratio*95% CI
Age group (yrs)
Chlamydia test type
One or more sexual
One or more clinical findings‡
Chlamydia in last 12 mo
Partner with chlamydia
Pregnancy related visit
*Adjusted for age, test type, sexual behavioral risks, clinical exam
findings, partner with chlamydia, chlamydia in past 12 month, and
pregnancy related visit.
†Includes having had a new sex partner, multiple sex partners, or
symptomatic sex partner in the past 60 days.
‡Includes mucopurulent cervicitis, friable cervix, ectopy, and pelvic
inflammatory disease (PID).
Sexually Transmitted Diseases ● December 2008
GORGOS ET AL.
In summary, AI/AN women continue to suffer from a higher
burden of disease caused by CT, as amply demonstrated in our
analysis. The explanation for this differential remains unclear.
Further investigation of risk factors for CT, related outcomes includ-
ing pelvic inflammatory disease and tubal infertility, access to screen-
ing and treatment, sexual networks, more effective approaches to
partner management, and more widespread surveillance would be
beneficial to future health improvement and disease control measures
in this vulnerable population.
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