Diagnostic accuracy of an enzyme-based point-of-care test versus Nugent score for bacterial vaginosis among pregnant women attending routine antenatal care in Zambia.

BACKGROUND

Bacterial vaginosis (BV) is associated with adverse pregnancy outcomes. OSOM® BVBlue® is a chromogenic point-of-care (POC) test that detects sialidase, an enzyme produced by Gardnerella vaginalis and some other anaerobic bacteria associated with BV. This study, part of the World Health Organization’s global ProSPeRo study, aimed to evaluate the performance of this POC test compared with the Nugent score reference standard among pregnant women in Zambia. Additionally, the operational characteristics and patient acceptability of the POC test were evaluated.

METHODS

Pregnant women attending four health centres in Nchelenge, Zambia, for antenatal care between 15 February and 26 May 2023 participated. Clinician-collected vaginal swabs for OSOM® BVBlue® and Nugent scoring were obtained from each participant. POC test results were read independently by two staff members. Study staff completed a questionnaire on the operational characteristics of the POC test, whereas participants were asked about the length of time that they would be willing to wait for POC test results.

RESULTS

Paired POC and reference test vaginal swabs from 999 participants were analysed. Overall, 23.1% (231/999) tested positive for BV by Nugent score. Overall sensitivity and specificity of OSOM® BVBlue® were 41.3% (95% confidence interval [CI] 25.4–59.2%) and 93.1% (95% CI 89.8–95.4%), respectively. Inter-rater agreement was 99.6% (Cohen’s Kappa 0.984). Most pregnant women, 97.9% (978/999), were willing to wait up to 20 min for a POC test result, and 59.2% (591/999) up to 30 min. Of 14 study staff members, all found the POC test easy to use and instructions clear, 13 felt the results were easy to interpret, with 12 reporting test results were available within 25 min. Cold-chain requirements and short shelf life were perceived as significant challenges.

CONCLUSION

Overall, OSOM® BVBlue® yielded sub-optimal sensitivity. The findings from this study are valuable for the development of minimal and optimal product profiles for POC tests for BV. These profiles, in turn, may guide future research and development for this prevalent condition with important sexual and reproductive health consequences. Logistical challenges need to be addressed for effective implementation of POC testing in resource-limited settings. TRIAL REGISTRATION: PACTR202302766902029.