Evaluation of a Modified Sanitary Napkin as a Sample Self-Collection Device for the Detection of Genital Chlamydial Infection in Women
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JOURNAL OF CLINICAL MICROBIOLOGY, July. 2001, p. 2508–2512 Vol. 39, No. 7
0095-1137/01/$04.00⫹0 DOI: 10.1128/JCM.39.7.2508–2512.2001
Copyright © 2001, American Society for Microbiology. All Rights Reserved.
Evaluation of a Modified Sanitary Napkin as a Sample
Self-Collection Device for the Detection of Genital
Chlamydial Infection in Women
MICHEL ALARY,1,2* CÉLINE POULIN,1 CÉLINE BOUCHARD,3 MICHEL FORTIER,3
GILLES MURRAY,4 SUZANNE GINGRAS,4 MICHEL AUBÉ,5 AND CAROL MORIN5
Direction Régionale de la Santé Publique de Québec,1 Groupe de Recherche en Épidémiologie de l’Université Laval,
Centre de Recherche,2 and Departments of Obstetrics and Gynaecology,3 Microbiology,4 and Pathology,5
Hôpital du St-Sacrement du Centre Hospitalier Affilié Universitaire de Québec, Québec, Canada
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Received 20 November 2000/Returned for modification 22 February 2001/Accepted 2 May 2001
A modified sanitary napkin was compared with endocervical swab and urine specimens for the detection of
urogenital Chlamydia trachomatis infection. Endocervical swabs and/or first-catch urine were collected from 510
women at medical or community settings in Quebec City. Participants were also asked to wear a modified
sanitary napkin (Ezy-Detek) during 4 consecutive hours and to bring it back to the clinic or mail it to the
laboratory. Endocervical and urine specimens were tested using the Cobas Amplicor CT/NG assay (Roche
Diagnostic Systems) according to the manufacturer’s instructions, as were specimens collected with the napkin
after adequate preparation. If the PCR test result was positive on the endocervical sample or on any two
samples, a woman was considered to be infected. PCR testing results on paired samples were identical for 493
(96.6%) of 510 women. According to the definition given above, 58 (11.3%; 95% confidence interval [CI], 8.7 to
14.5%) women were infected with C. trachomatis. The sensitivity and specificity of PCR testing on modified
sanitary napkin specimens were, respectively, 93.1% (54 of 58; 95% CI, 83.3 to 98.1%) and 98.9% (447 of 452;
95% CI, 97.4 to 99.6%) compared to 81.0% (47 of 58; 95% CI, 68.6 to 90.1%) and 100% (451 of 451; 95% CI, 99.2
to 100%) for urine specimens. The positive and negative predictive values were, respectively, 91.5% (54 of 59)
and 99.1% (447 of 451) for the sanitary napkin specimens compared to 100% (47 of 47) and 97.6% (451 of 462)
for urine samples. These results suggest that a modified sanitary napkin represents an effective noninvasive
device for self-collection of specimens to detect urogenital C. trachomatis infection.
Chlamydia trachomatis infection is the most frequently re- swabbing, which necessitates vaginal speculum insertion and a
ported sexually transmitted disease in the industrialized coun- gynecologic examination. In a study, as many as 60% of chla-
tries. The association of this infection with transmission of mydia-infected adolescents would have been missed if the
human immunodeficiency virus infection, pelvic inflammatory urine screening program had not been in place, because they
disease, infertility, ectopic pregnancy, and chronic pelvic pain refused the gynecologic examination (14). In addition, speci-
(10, 20, 30) constitutes a major public health concern. Because mens may be collected in nontraditional medical settings, such
most infected women have no specific symptoms or are asymp- as community centers and schools, and eventually at home (6,
tomatic, screening programs represent one of the main ap- 11, 15, 17). Although these methods have been shown to be
proaches to control this infection (20, 21). relatively easy to use and sensitive for the detection of C.
The current literature provides very good information on the trachomatis, some women failed to collect adequate specimens
value of gene amplification techniques, such as PCR or ligase or did not feel at ease with the technique (2, 16, 31). The
chain reaction, for the detection of C. trachomatis in the lower objective of the present study was to evaluate a modified san-
genital tracts of women. Both technologies have been evalu- itary napkin (Ezy-Detek [EDI] Inc., Sillery, Canada) as a spec-
ated in depth using endocervical swab or urine samples. With imen self-collection device for detection of chlamydial infec-
a specificity higher than 98%, the sensitivity of PCR on either tion in women. Results of PCR tests on sanitary napkin
cervical specimens or urine samples varies from 80.0 to 100% specimens were compared with those for endocervical and
(4, 12, 18, 19, 27, 28). urine specimens obtained from the same women.
More recently, detection of chlamydial infection by these
techniques has also been assessed on secretions recovered MATERIALS AND METHODS
from vaginal introitus collected by clinicians or patients them-
Study population and specimen collection. The study population consisted of
selves (2, 5, 9, 15, 16, 22, 26, 31, 33) or from vaginal tampons women at different medical or community settings in Quebec City. Women were
(13, 23–25). Urine and self-collected samples represent easy recruited through family-planning clinics, teen clinics, and a public juvenile
and noninvasive techniques compared to the usual cervical facility health service. Each of these women had a gynecologic examination, and
an endocervical swab specimen was taken for C. trachomatis detection as part of
the medical visit. In order to include a sufficient number of infected women,
physicians from private medical clinics who received positive chlamydia test
* Corresponding author. Mailing address: Centre de Recherche, results for their patients were also invited to collaborate by asking infected
Hôpital du Saint-Sacrement du CHA, 1050, chemin Ste-Foy, Québec women to participate in the study before treatment.
(Qc), Canada G1S 4L8. Phone: (418) 682-7387. Fax: (418) 682-7949. After giving written informed consent, participants were asked to complete an
E-mail: michel.alary@gre.ulaval.ca. anonymous short questionnaire on risk behavior and medical history and to
2508VOL. 39, 2001 C. TRACHOMATIS DETECTION IN SANITARY NAPKIN SPECIMENS 2509
provide a urine specimen. First-catch urine (15 to 30 ml) was collected in a assume any gold standard (29). According to each definition, relative sensitivity
screw-cap plastic jar, placed in plastic bags, and refrigerated until transport to the and specificity, 95% confidence intervals (95% CI), and the positive and negative
laboratory (within 4 days of collection). The modified sanitary napkin comprises predictive values for PCR tests on sanitary napkin, urine, and endocervical swab
a conventional sanitary napkin which was modified by adding a removable sam- specimens were calculated. The sensitivity and specificity of PCR on each type of
pling filter between the upper porous and lower impermeable sheets. This device specimen were also calculated according to the latent class model.
was provided to women with a postage-paid, preaddressed envelope. Women
were asked to wear the modified sanitary napkin for a period of 4 consecutive
hours during their usual activities (determined by a pretest study among 15 RESULTS
women with recently diagnosed chlamydial infections and 4 uninfected women)
and then to put it in the plastic bag provided, writing the date and the times at From September 1999 to May 2000, 510 women participated
which they put on and took off the napkin on the label. They could bring the in the study: 246 (48.2%) were recruited through medical clin-
envelope back to the recruitment site or mail it to the laboratory. Infected ics, among whom 24 were enrolled after laboratory-diagnosed
women who were enrolled at a medical visit at which they received a drug but untreated chlamydial infection; 157 (30.8%) were high
prescription were asked to provide a urine specimen and to wear the sanitary
napkin before taking their treatment.
school students; and 107 (20.9%) were incarcerated adoles-
In order to assess the specimen self-collection device in a nonmedical context, cents or street youth. Another 54 women (39 from medical
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a community-based organization providing services to street youth and a high- clinics, 10 from high school, and 5 street youth or incarcerated
school-based clinic were asked to collaborate in the study. In these settings, C. adolescents) who provided endocervical and/or urine speci-
trachomatis screening was performed on urine specimens. In the context of the mens were excluded because they did not mail or bring back
present study, these young women were also asked to wear the sanitary napkin
as described above. In these groups, women with positive PCR test results were
the sanitary napkin. Most (90.6%) participants were less than
invited to visit their physicians for adequate follow-up and treatment. A gyne- 25 years old. A history of sexually transmitted disease (STD)
cological examination was performed and a cervical swab specimen was taken was reported by 23.9% (122 of 510) of participants, while 4.3%
before treatment. Exclusion criteria were being younger than 14 years, under (22 of 510) reported having had a sexual partner infected with
antibiotherapy, or menstruating. Those with active severe vulvitis or known
an STD in the previous 6 months. In addition, 12.6% (64 of
intolerance of sanitary napkins were also excluded.
Questionnaires and specimens were coded. The code number was written on 510) of women reported genital symptoms at their enrollment,
the consent form in order to identify the subject. Only the medical team had such as vaginal discharge, abdominal pain, and a variety of
access to name information. Medical examination and free treatments were other complaints.
available at recruitment sites or at local community health clinics. The study A total of 294 women provided matched endocervical, urine,
protocol was approved by the Ethics Committee of the Hôpital du St-Sacrement
du Centre Hospitalier Affilié Universitaire and the Centre Hospitalier Univer-
and sanitary napkin specimens, and 215 participants provided
sitaire de Québec-CHUL. only urine and sanitary napkin specimens, whereas cervical
Laboratory procedures. The Amplicor PCR assay (Roche Diagnostic Systems, swab and sanitary napkin specimens were collected from 1
Inc., Branchburg, N.J.) was performed on both cervical and urine specimens woman. Three hundred forty-two women (67.1%) sent in their
within 5 days of collection. The sanitary napkins were kept at room temperature
sanitary napkins by mail, while 168 (32.9%) brought them back
until their preparation. At the time of testing, the filter of the sanitary napkin was
transferred into a 50-ml polypropylene tube containing 2 ml of Amplicor collec- to the recruitment site. According to the information on the
tion transport medium and vigorously agitated for 15 min. This preparation was label, 96.1% women wore the sanitary napkin for at least 4 h.
done in a separate room from that used for PCR analysis. All samples were then While cervical and urine specimens were tested within 5 days
processed by the Cobas Amplicor system according to the manufacturer’s in- of collection, sanitary napkin specimens were processed from 1
structions.
Chlamydial DNA detection with the Amplicor diagnostic kit is based on three
to 82 days of collection (median, 9 days; 98.7% within 30 days).
different steps: (i) PCR amplification, (ii) hybridization with a C. trachomatis- Overall, 64 (5.0%) of 1,286 PCR specimens were found to be
specific probe, and (iii) detection of amplified material by a colorimetric reaction inhibitory at initial testing (this information was missing for 20
secondary to enzymatic reaction. The internal control DNA included in the endocervical, 5 urine, and 3 sanitary napkin samples). The
Cobas Amplicor system was used to monitor the inhibition of amplification.
inhibition rates were 4.4% (12 of 275), 4.4% (22 of 504) and
Optical density (OD) was read on a spectrophotometer at 450 nm. OD values
below 0.2 meant a negative result if the internal control was positive. Values 5.9% (30 of 507) for endocervical, urine, and sanitary napkin
equal to or greater than 0.8 meant a positive result, regardless of the internal specimens, respectively. PCR inhibitors were removed after
control result. In order to avoid ambiguity, specimens interpreted as positive and dilution in 61 of 64 initially inhibitory samples, while the three
those with OD values between 0.2 and 0.8 interpreted as equivocal results were other samples (one urine and two sanitary napkin specimens)
reprocessed and reanalyzed, and their results were established according to the
required heating at 100°C after dilution to eliminate the inhi-
above definition. When the internal control was negative, indicating the presence
of DNA inhibitors, aliquots of the original specimens were retested after 1:10 bition. Retested samples confirmed positive results for eight
dilution or heating at 100°C for 15 min. Paired specimens with discordant results endocervical and seven sanitary napkin specimens and yielded
were retested by processing another aliquot of each original specimen. additional positive results for two endocervical, one urine, and
Statistical analysis. With the advent of DNA amplification tests which have five sanitary napkin specimens. Altogether, PCR test results on
better sensitivity than culture, different combinations of alternative tests were
used as an expanded reference standard for the calculation of the performance
paired samples were identical for 96.6% (493 of 510) of par-
characteristics of a new technique, because no “gold standard” has been defined ticipants (94.9 and 99.0% of those who provided three and two
yet (1). Different methods used to resolve discrepant results have also been samples, respectively) (Table 1). This proportion was similar
criticized (7, 8). In the present study, the performance characteristics of PCR in for women who mailed their sanitary napkins in and those who
different specimens was calculated in three ways. First, only women with a
brought them back to the recruitment site (96.5 versus 97.0%)
positive PCR test result on the endocervical swab specimen were considered
truly infected. This definition was based on the fact that, from a clinical point of and for the sanitary napkin specimens analyzed within 10 days
view, PCR testing on endocervical swab specimens is currently used for the of collection versus the others (97% in each instance).
diagnosis of C. trachomatis infection in Quebec City. Because PCR testing on The PCR test results were positive on two or three paired
urine samples is available for specific groups of women, such as street youth and samples (accordingly) from 46 women (Table 1). In addition,
prostitutes, who are often reluctant to attend traditional medical settings, women
with positive PCR test results on both urine and sanitary napkin specimens were
12 of 17 women with discrepant PCR test results were consid-
also considered truly infected in the second analysis. Finally, PCR testing on the ered infected because the endocervical swab specimen or at
three types of specimens was assessed using a latent class model which did not least two specimen types tested positive by PCR. Overall, 392510 ALARY ET AL. J. CLIN. MICROBIOL.
TABLE 1. Results of C. trachomatis testing by PCR on trachomatis positive; one of these had a negative PCR test on
endocervical swab, urine, and modified sanitary napkin specimens the endocervical swab specimen. Unfortunately, the other six
collected from 510 women in Quebec City, Canada
women did not provide endocervical swab specimens (Table
No. of women Resulta by PCR test on specimen type 1). Four women had a positive PCR test on the endocervical
with profile Endocervical Urine Sanitary napkin swab specimen and a negative PCR test on urine and sanitary
napkin specimens, while three others had a positive PCR test
239 ⫺ ⫺ ⫺ on the sanitary napkin sample and a negative PCR test on
207 NA ⫺ ⫺
1 ⫺ NA ⫺ urine and endocervical swab specimens (Table 1).
3b,c ⫺ ⫺ ⫹ The performance characteristics of PCR for each type of
2b,c NA ⫺ ⫹ specimen, calculated by using either a positive endocervical
40 ⫹ ⫹ ⫹ swab specimen exclusively or at least two positive specimens as
6 NA ⫹ ⫹
a standard, are presented in Table 2, as well as the sensitivity
7b,d ⫹ ⫺ ⫹
4b,d ⫹ ⫺ ⫺ and specificity obtained with the latent class model. The sen-
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1b,d ⫺ ⫹ ⫹ sitivity of PCR on sanitary napkin specimens was higher than
that on urine samples (92 to 100% versus 78 to 85%), whereas
Total 295 509 510 the relative specificities were comparable (98 to 99% and 99 to
a
⫺, negative; ⫹, positive; NA, not available. 100%, respectively). These results did not change significantly
b
These samples produced discrepant results on one or two specimen types. when symptomatic and asymptomatic infected women were
c
These women were classified as not infected with C. trachomatis because they
had a negative PCR test result on the endocervical swab specimen or they had a compared (data not shown).
positive PCR test result on only one specimen.
d
These women were classified as infected with C. trachomatis because they
had a positive PCR test result on the endocervical swab specimen or on at least DISCUSSION
two specimens.
The results of the present study suggest that a modified
sanitary napkin may represent an effective specimen self-col-
(15.9%) of 246 women recruited through medical clinics were lection device for the detection of C. trachomatis infection by
infected with C. trachomatis (of whom 24 were enrolled after a PCR. Using a positive PCR test on endocervical swab speci-
recent positive test result), as were 2 (1.3%) of 157 high school mens exclusively or in combination with positive results from at
students and 17 (15.9%) of 107 incarcerated adolescents or least two specimens to identify infected patients, or using the
street youth. A minority (18 of 58) of infected women reported latent class model that does not assume any gold standard (29),
symptoms such as vaginal discharge (10 women), abdominal the relative sensitivity and specificity of PCR on sanitary nap-
pain (3 women), and different other complaints (5 women). kin specimens were 92 to 100% and 98 to 99%, respectively.
Forty-seven (92.2%) of 51 women who were C. trachomatis These values are similar to those reported with vaginal swab
positive by PCR on the endocervical swab specimen also had a specimens obtained by health care providers (22, 26, 31, 33)
positive PCR test on the sanitary napkin specimen. In symp- and are similar to or slightly higher than those reported with
tomatic and asymptomatic women, these rates were, respec- self-collected vaginal swab specimens (2, 5, 9, 15, 16, 31) or
tively, 94.4% (17 of 18) and 90.9% (30 of 33). For seven vaginal tampon specimens (13, 23–25).
participants, both urine and sanitary napkin specimens were C. In the present study, the results show that C. trachomatis
TABLE 2. Performance characteristics for detection of C. trachomatis by PCR in each type of specimen, according to the definition of
infection used as a reference standard, among women from Quebec City, Canada
Reference standard and specimen Sensitivitya (95% CI) Specificityb (95% CI) PPVc NPVd
Positive PCR on endocervical swab
Sanitary napkin (n ⫽ 295) 92.1; 47/51 (81.1–97.8) 98.4; 240/244 (95.9–99.6) 92.1 (47/51) 98.4 (240/244)
Urine (n ⫽ 294) 78.4; 40/51 (64.7–88.7) 99.6; 242/243 (97.7–100) 97.6 (40/41) 95.7 (242/253)
Endocervical swab NAe NA NA NA
Positive PCR on endocervical swab or on at least 2
specimens
Sanitary napkin (n ⫽ 510) 93.1; 54/58 (83.3–98.1) 98.9; 447/452 (97.4–99.6) 91.5 (54/59) 99.1 (447/451)
Urine (n ⫽ 509) 81.0; 47/58 (68.6–90.1) 100; 451/451 (99.2–100) 100 (47/47) 97.6 (451/462)
Endocervical swab (n ⫽ 295) 97.9; 47/48 (88.9–99.9) 100; 247/247 (98.5–100) 100 (47/47) 99.6 (247/248)
No reference standard (latent class, model) (n ⫽ 294
for all specimens)
Sanitary napkin 100 98.8 (97.4–99.8) NA NA
Urine 85.2 (75.0–95.4) 100 NA NA
Endocervical swab 97.6 (92.8–97.7) 98.4 (96.8–100) NA NA
a
Values are percentages. Where a second value is listed, it is the number of specimens that were true positive/(number true positive plus the number true negative).
b
Values are percentages. Where a second value is listed, it is the number of specimens that were true negative/(number true negative plus the number false positive).
c
PPV, positive predictive value. Values are percentages, with the number of specimens that were true positive/(the number true positive plus the number false
positive) given in parentheses.
d
NPV, negative predictive value. Values are percentages, with the number of specimens that were true negative/(the number true negative plus the number false
negative) given in parentheses.
e
NA, not applicable.VOL. 39, 2001 C. TRACHOMATIS DETECTION IN SANITARY NAPKIN SPECIMENS 2511
infection was more likely to be detected in sanitary napkin presented symptoms clinically consistent with C. trachomatis
specimens than in urine specimens. As previously reported, the infection. False-positive results with sanitary napkins are pos-
sensitivity of DNA techniques on female urine samples may be sible, but false-negative results from endocervical swab speci-
suboptimal because C. trachomatis infection is localized in the mens related to inadequate specimen collection may also ex-
uterine cervix in most women (21). Conversely, some infected plain these discrepant results (1, 3). Sanitary napkin specimens
women may harbor C. trachomatis only in the urethra, and this from two women who did not provide endocervical swab spec-
infection may be missed by testing only endocervical or vaginal imens were positive, whereas urine samples was negative.
swab specimens (4, 6, 15, 18, 19, 27, 28). Thus, testing on single These women were considered noninfected in the calculation
specimens (either urogenital or urine samples) may fail to of the performance characteristics of PCR on sanitary napkin
identify all infected women (4, 15, 18, 19, 32). specimens.
It has been suggested that vaginal swabs may collect biologic The results of the present study suggest that a modified
material from both the cervix and the urethra (31). However, sanitary napkin represents an easy, noninvasive, and efficient
when the performance of different self-collected samples had specimen self-collection device for C. trachomatis testing by
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been assessed, the sensitivity of PCR on combined urine and PCR. It may be particularly useful for screening programs in
vaginal swab specimens was 96%, compared to 83% when PCR nonclinical settings, allowing for the provision of STD services
was performed only on vaginal swab specimens and 74% when to high-risk groups, such as incarcerated adolescents, street
it was performed only on first-catch urine samples (15). In the youth, and persons involved in prostitution who are not in-
same way, the sensitivity of a C. trachomatis PCR test on a clined to attend traditional medical settings. Since this device
combined urine and cervical swab specimen was higher com- allows very easy self-collection of specimens, it could also be
pared to testing on separate samples (32). It would be inter- useful to increase the accessibility of C. trachomatis screening
esting to assess the performance of the sanitary napkin speci- for women in general. Further studies are required to evaluate
men compared to that of the corresponding self-collected whether this specimen self-collection device may represent an
vaginal swab specimen in detecting C. trachomatis infection in accurate and cost-effective approach to the detection not only
women. Unfortunately, self-taken vaginal introitus swab spec- of C. trachomatis but also of other STDs.
imens were not collected in the present study because the
requirement for too many types of samples to be provided by ACKNOWLEDGMENTS
the women could have led to low participation rates. Further
We thank the collaborating physicians as well as the directors and
studies would be needed to assess women’s attitudes to these staff of collaborating organizations: Les Oeuvres de la Maison Dau-
different sampling methods and to evaluate whether sanitary phine Inc.; the Centre-Jeunesse de Québec, I’Escale; the Collège St-
napkin specimens represent an efficient alternative to sampling François-Xavier Garneau; the CEGEP Ste-Foy; the Clinique de Plani-
of multiple sites and may thus improve the cost-effectiveness of fication des Naissances of the Hôpital St-François d’Assise and of the
urogenital C. trachomatis infection diagnosis in women. Sani- Centre Hospitalier Universitaire Laval du Centre Hospitalier Univer-
sitaire de Québec; the CLSC Haute-Ville, Basse-Ville/Limoilou; and
tary napkins represent additional important advantages. They CLSC La Source, Quebec City, Canada. We also acknowledge Roche
are a common product previously used by almost all women, Diagnostic Systems, Inc. for providing AMPLICOR CT/NG test kits
and they have less-stringent transport criteria than urine or and EZY-Detek (EDI) Inc. for providing modified sanitary napkins.
endocervical and vaginal swab specimens. Indeed, in the pre- This study was supported by the Division of STD Prevention &
Control, Bureau of HIV/AIDS, STD & TB, Laboratory Centre for
test study, sanitary napkin samples were kept at room temper- Disease Control, Health Canada. M. Alary is a research scholar of the
ature for up to 6 weeks before being tested without alteration Fonds de la Recherche en Santé du Québec (970097-103).
in the PCR testing results (data not shown).
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