Date: June 25th, 2021

Guest Skeptic: Dr. Chris Bond is an emergency medicine physician and assistant Professor at the University of Calgary. He is also an avid FOAM supporter/producer through various online outlets including TheSGEM.

Reference: Chinnock et al. Self-obtained vaginal swabs are not inferior to provider-performed endocervical sampling for emergency department diagnosis of Neisseria gonorrhoeae and Chlamydia trachomatis. AEM June 2021

Case: A 31-year-old female presents to the emergency department with pelvic pain and vaginal discharge for the past 24 hours. She is afebrile, vital signs are normal and she is having a significant amount of pain. She says the pain is so severe that she cannot even imagine having a pelvic exam done right now for STI testing.

Background: Neisseria gonorrhoeae (NG) and Chlamydia trachomatis (CT) are the two most common sexually transmitted infections (STI) reported in the United States. Emergency departments (EDs) now diagnose an increasing percentage of NG/CT cases compared to STI clinics. (1,2)

The standard of care for NG/CT diagnosis is nucleic acid amplification testing (NAAT), with the collection method being provider-performed endocervical sampling (PPES). PPES is uncomfortable for patients and has numerous other limitations, including the need for exam rooms, an available provider and often a female chaperone. These limitations can delay sample collection and can also add significant delay in a busy ED. The need for universal pelvic examination in the ED to perform STI testing has also come under increasing scrutiny. (3)

Vaginal sample collection with self-obtained vaginal swabs (SOVS) was first developed and researched in non-ED settings based on these reasons and others. These studies demonstrated comparable sensitivity for NG/CT diagnosis when comparing SOVS to PPES, and high patient acceptability. (4-8)

However, those studies were performed in a wide range of non-ED settings and were mostly asymptomatic screening rather than STI testing in an acute care environment. This study compares PPES with SOVS in an ED setting and explores patient’s acceptability or preference of SOVS versus PPES.

Clinical Question: Do self-obtained swabs have noninferior sensitivity for the diagnosis of NG/CT compared to provider performed swabs in an ED setting using a rapid NAAT.

Reference: Chinnock et al. Self-obtained vaginal swabs are not inferior to provider-performed endocervical sampling for emergency department diagnosis of Neisseria gonorrhoeae and Chlamydia trachomatis. AEM June 2021

  • Population: Female patients 18 years of age or older who were judged by the treating practitioner to need NG/CT testing
    • Exclusions: Incarcerated any acute psychiatric condition precluded understanding instructions or giving informed consent, not English or Spanish proficient, or treated for NG/CT within the previous four weeks.
  • Intervention: Self-obtained vaginal swab (SOVS) for NG/CT
  • Comparison: Provider performed endocervical sampling swab for NG/CT
  • Outcome:
    • Primary Outcome: Noninferiority of SOVS sensitivity for NG/CT, with noninferiority being demonstrated if sensitivity was 90% or above.
    • Secondary Outcomes: Kappa measurement of the SOVS and PPES, SOVS organism-specific sensitivity for NG and CT, acceptance rate of SOVS, rate of patients worried about doing SOVS correctly, and SOVS refusal rate.

Dr. Brian Chinnock

This is an SGEMHOP episode which means we have the lead author on the show. Dr Brian Chinnock is Professor in Department of Emergency Medicine at the UCSF-Fresno Medical Education Program, and Research Director.

Authors’ Conclusions: SOVS are noninferior to PPES in NG/CT diagnosis using a rapid NAAT in ED patients and surveys indicate high patient acceptability.”

Quality Checklist for Observational Trials:

  1. Did the study address a clearly focused issue? Yes
  2. Did the authors use an appropriate method to answer their question? Yes
  3. Was the cohort recruited in an acceptable way? Yes
  4. Was the exposure accurately measured to minimize bias? Yes
  5. Was the outcome accurately measured to minimize bias? Yes
  6. Have the authors identified all important confounding factors? Yes
  7. Was the follow up of subjects complete enough? Yes
  8. How precise are the results/is the estimate of risk? The results are precise with narrow confidence intervals
  9. Do you believe the results? Yes
  10. Can the results be applied to the local population? Yes
  11. Do the results of this study fit with other available evidence? Yes

Results: The researchers found 750 patients eligible for inclusion in the study. The final cohort consisted of 515 patents with completed PPES and the SOVS results. The mean age was 30.7 years of age with 52% Hispanic ethnicity. The overall prevalence for either NG or CT or both was 17% (86/515). Of these patients with STIs, 34% (29/86) had infection with NG, 54% (47/86)) with CT, and 12% (10/87) with coinfection.

Key Result: SOVS was non-inferior to PPES

  • Primary Outcome: Noninferiority of SOVS sensitivity for NG/CT
    • SOVS had a sensitivity of 95% (95% CI, 88% to 99%) for the detection of NG/CT when compared to PPES.
  • Secondary Outcomes:
    • Kappa was 93 (95% CI, 0.89 to 0.98), which is excellent.
    • SOVS Sensitivity for NG and CT was 97% (95% CI = 87% to 100%) and 94% (95% CI = 84% to 99%) respectively
    • 93% felt that collecting a self-sample is acceptable
    • 28% who were concerned about doing SOVS incorrectl
    • 26% refused SOVS due to reasons clearly related to the SOVS collection procedure (“uncomfortable performing SOVS,” “worried might do it incorrectly”, “prefers physician”) rather than the consent process.

Here are the ten nerdy questions we asked Brian to help us better understand his study. Listen to his respond to each question on the SGEM podcast.

1. Selection Bias: Convenience sample (not overnight). Do you think that could have had an impact on your results?

2. Exclusions: Why were patients excluded if they had been treated for NG/CT in the previous 4 weeks?

3. Non-Inferiority: Why do a non-inferiority study design instead of a superiority design?

4. Endocervical Swabs: These were endocervical swabs used in the provide performed exam but would have been vaginal swabs if done by patients themselves. So, are endocervical swabs not actually required to be endocervical?

5. Power: The power was set based on the manufacturer’s reported sensitivity for PPES using the Cepheid Xpert assay of 99% for NG, 96% for CT and a presumed combination of 97%. Non-inferiority was set at 7% with an assumed prevalence of 14% based on the previous year’s data. This required a target of 571 patients or 615 if you only had a prevalence of 13%. You missed the overall target but did get at least 80 positive patients. Can you explain why you stopped enrollment, and do you think it would impact your study?

6. Aptima: Where I work, we use Aptima endovaginal swabs for STI testing, and I assume this would be even better for self-testing than swabs that require endocervical sampling. Are there other studies that support this hypothesis?

7. Best Swab Type: Is there a list of swab types that would be effective for SOVS vs. PPES? Yours is a 90-minute NAAT swab which is not used in many centers and the swabs used can vary by geographic location.

8. External Validity: In the limitations section, you mention the high proportion of Hispanic (52%) ethnicity as making the study potentially not generalizable to all ED settings. Can you explain why this would be?

9. Qualitative: Can you discuss the qualitative data as to reasons why patients declined to participate in the study and why some still preferred a provider performed exam to a self-obtained swab?

10 Anything Else: We like to have an open-ended question to allow the author to discuss something that we did not address in our nerdy questions. Is there anything else you would like to add about your study?

Comment on Authors’ Conclusion Compared to SGEM Conclusion: We generally agree with the authors’ conclusions.

SGEM Bottom Line: Consider the use of self-obtained vaginal swabs for STI testing and the necessity of performing a pelvic exam for patients presenting with clinical suspicion for NG/CT.

Case Resolution: You provide your patient with analgesic for her pain and ask if she would prefer a self-obtained vaginal swab or for you to perform a pelvic exam to obtain a swab. She chooses to perform the swab herself, and you treat her empirically for an NG/CT.

Dr. Chris Bond

Clinical Application: This was an excellent study that supports the use of self-obtained vaginal swabs for STI testing in the ED and can reduce uncomfortable pelvic exams for patients. It is reasonable to offer this option to patients presenting to the ED who clinically require a swab for STI testing but there is no other need for a pelvic examination.

What Do I Tell My Patient? I am concerned that you may have an STI. A vaginal swab should be done to test for this infection. Doing a vaginal swab by yourself is just as accurate as having me perform a pelvic exam. It will also be faster and probably less painful for you. I understand if you are uncomfortable doing it yourself. I am happy to do the exam and get the swab sample. It is your choice and both options are fine.

Keener Kontest: Last weeks’ winner was Dr. Sebastian Nemetz from Offenbach, Germany. He knew Dr. Emil Siegle is the German physician is credited with the creation of pneumatic otoscopy?

Listen to the podcast this week to hear the trivia question. Email your answer to with “keener” in the subject line. The first correct answer will receive a cool skeptical prize.

SGEMHOP: Now it is your turn SGEMers. What do you think of this episode on the use of self-obtained vaginal swabs? Tweet your comments using #SGEMHOP.  What questions do you have for Brian and his team? Ask them on the SGEM blog. The best social media feedback will be published in AEM.

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Remember to be skeptical of anything you learn, even if you heard it on the Skeptics’ Guide to Emergency Medicine.