Self-collected versus provider-collected vaginal swabs for the diagnosis of bacterial vaginosis: an assessment of validity and reliability

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Abstract

Bacterial vaginosis (BV) in pregnancy is related to numerous adverse events; however, the validity of different methods of vaginal swab collection to diagnosis BV among pregnant women is unclear. This study examines the validity of self-collected compared with provider-collected vaginal swabs and describes the intra-rater and inter-rater reliability of BV assessment among a sample of pregnant women early in gestation. Gram-stain evaluation of vaginal samples using the Nugent criteria was conducted to determine the overall and morphotype-specific BV scores. We found strong validity for the overall and morphotype-specific scores comparing self-collected swabs to provider-collected swabs. In addition, we found excellent overall and morphotype-specific inter-rater reliability and excellent intra-rater reliability in our sample. These study results support the use of self-collected vaginal swabs for diagnosing BV and document the reliability of BV assessment among pregnant women.

Introduction

Bacterial vaginosis (BV) is a vaginal condition involving a reduction in the normal amount of hydrogen-peroxide producing Lactobacillus and an overgrowth of anaerobic and Gram-negative or Gram-variable bacteria, including Mycoplasma hominis, Bacteroides spp., Mobiluncus spp., and Gardnerella vaginalis[1], [2]. BV is a prevalent condition and is the number one cause of vaginitis among pregnant and nonpregnant women, with current studies reporting 10% to 50% of pregnant women positive for BV [3], [4], [5], [6], [7]. BV has been related to numerous adverse pregnancy outcomes, including preterm labor, preterm delivery, and premature rupture of the membranes [8], [9], [10]. One study examining BV diagnosed during the first trimester of pregnancy reported a 2.6-fold increased risk for preterm labor (95% confidence interval [CI] 1.3–4.9), a 6.9-fold increased risk for preterm delivery (95% CI 2.5–18.8), and a 7.3-fold increased risk for preterm premature rupture of the membranes (95% CI 1.8–29.4) [8]. In addition, recent studies have reported a 3- to 5-fold increased risk of spontaneous abortion among pregnant women with bacterial vaginosis, although these studies were hampered by small sample size and were limited to high-risk pregnant women [11], [12], [13].

One of the most commonly used diagnostic tests for BV is a Gram-stain microscopic evaluation of vaginal secretions and an assessment of the relative concentrations of bacterial morphotypes consistent with Lactobacillus spp., Mobiluncus ssp., Gardnerella, and other anaerobic bacteria, such as Bacteroides spp. [14]. Generally, vaginal swabs used for BV detection are collected by the provider during a pelvic examination; however, using self-collected vaginal swabs may be attractive for epidemiologic studies. Obtaining self-collected samples does not require recruiting study participants from clinical settings, facilitates repeat sampling for studies designed to measure BV status at multiple points in time, and is time- and cost-efficient. Several studies have used self-collection as the method of obtaining vaginal swabs [15], [16], [17], [18], but only one small study examined the validity of self- compared with provider-collected swabs to diagnosis BV. This study was limited to a small number of nonpregnant women [15]. In this study, specimens were collected during the menstrual cycle of 18 premenopausal, nonpregnant women and indicated a high agreement of bacterial vaginosis identification among self-collected versus provider-collected swabs (r = 0.74, P<.001). Anecdotal evidence suggests that the prevalence of BV is higher among pregnant women, perhaps due in part to the dramatic hormonal changes occurring during pregnancy that influence the quantity of vaginal microbes present in the vagina; therefore, examining the validity of self- compared with provider-collected swabs in this population is particularly important.

We are currently conducting a large clinic-based prospective cohort study to determine the relationship between BV identified in the first trimester of pregnancy and the subsequent risk of spontaneous abortion among a group of pregnant women seeking prenatal care. We are assessing BV status among study participants by collecting a vaginal swab, either provider collected or self-collected, and using the Nugent criteria to document BV status. In this article, we report the validity of self-collected compared with provider-collected vaginal swabs and describe the intra-rater and inter-rater reliability of BV assessment for a sample of women who agreed to participate in our research project.

Section snippets

Patients

Women presenting for their first prenatal care visit to two different obstetrical practices at the Hospital of the University of Pennsylvania (HUP) who were less than 12 weeks gestation based on self-reported last menstrual period and resided within the city of Philadelphia were eligible to participate in the project. One recruitment site was a private obstetrical practice providing care to insured women; the other recruitment site was a public OB clinic. Nurse interviewers who were trained for

Results

Overall, the mean age of study participants was 24 years. Over 80% of the women were African American, 62% were single, 7% self-reported current cigarette smoking, and 27% reported a prior diagnosis of bacterial vaginosis. The mean gestational age at enrollment was 10 weeks, and the current prevalence of bacterial vaginosis in our study population was 48%.

Discussion

This study is the first to our knowledge to examine the validity of self-collected compared with provider-collected swabs to diagnose BV among pregnant women. We found that self-collected vaginal swabs have an excellent agreement for the overall diagnosis of BV among pregnant women compared with provider-collected swabs (kappa = 0.94). Our results are consistent with the study conducted by Schwebke et al., which examined the validity of self-collected compared with provider-collected swabs for BV

Acknowledgements

We thank Sara Keitzman, Lena Flower, Claire Barrett, and Katie McMahon for enrolling patients in the study, Jill Waldin and Carol Imperatrice for the microbiologic assessment of the slides, and Roberta Ness for her helpful comments on this manuscript. This work was supported by a grant from the National Institute of Child Health and Human Development (R01-HD-38856-01A1).

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