Assessment of Extrinsic Validity of HIV Oral Self-Test in A Low-Prevalence Population: A Bayesian Approach

Amit Nirmalkar; Amrita Rao; Megha Mamulwar; Mohan Kale; Uma Mahajan; Sandip Patil

doi:10.55489/njcm.160920255463

Authors

Amit Nirmalkar Division of Disease Elimination Sciences, ICMR- National Institute of Translation Virology and AIDS Research, Pune, India
Amrita Rao Division of Clinical Sciences, ICMR- National Institute of Translation Virology and AIDS Research, Pune, India
Megha Mamulwar Division of Disease Elimination Sciences, ICMR- National Institute of Translation Virology and AIDS Research, Pune, India
Mohan Kale Department of Statistics, Savitribai Phule Pune University, Pune, India
Uma Mahajan Independent Consultant, Pune, India
Sandip Patil Division of Clinical Sciences, ICMR- National Institute of Translation Virology and AIDS Research, Pune, India

DOI:

https://doi.org/10.55489/njcm.160920255463

Keywords:

Bayes, HIV Self-test, Sensitivity, Specificity, Extrinsic Validity

Abstract

Background: HIV oral self-test (HIVOST) is used for screening, particularly in diverse populations. While these tests offer convenience and privacy, their accuracy in low-prevalence settings remains a concern. A key measure of test reliability is extrinsic validity, which considers test sensitivity, specificity, and disease prevalence to determine the probability of true positivity given a positive test result. This statistical investigation aimed to evaluate the extrinsic validity of an HIVOST in a low-prevalence population.

Methodology: We applied Bayes' theorem to calculate the extrinsic validity of the HIVOST, incorporating test sensitivity, specificity, and the prevalence of HIV infection.

Important Findings: The analysis yielded an extrinsic validity of 7.70% (95% CI: 1.8% to 25%), meaning that in this low-prevalence setting, the probability of an individual truly having HIV after testing positive was relatively low. The participant who tests negative has a 99.97% (95% CI: 99.94% to 99.98%) chance of truly not having HIV, indicating high reliability of a negative result in this low-prevalence setting. Sensitivity analysis shows that PPV increases with prevalence, while NPV remains high, confirming the reliability of negative results across scenarios.

Conclusions: Although a positive HIVOST result strongly suggests HIV infection, the low extrinsic validity underscores the need for confirmatory testing, particularly in low-prevalence settings.

References

World Health Organization. Guidelines on HIV self-testing and partner notification: supplement to consolidated guidelines on HIV testing services. Geneva: WHO; 2016. Available from: https://iris.who.int/handle/10665/251655 [Accessed Apr 1st, 2025]

Rao A, Patil S, Nirmalkar A, et al. HIV oral self-screening test among HIV/STD/TB clinic attendees: A mixed-method pilot investigation examining merit for larger evaluation. Indian J Med Res. 2022;155(3-4):403-412. DOI: https://doi.org/10.4103/ijmr.ijmr_3131_21 PMid:35417993 PMCid:PMC9707688

Goligher EC, Heath A, Harhay MO. Bayesian statistics for clinical research. Lancet. 2024 Sep 14;404(10457):1067-1076. DOI: https://doi.org/10.1016/S0140-6736(24)01295-9 PMID: 39277290; PMCID: PMC12051211.

Bland JM, Altman DG. Bayesians and frequentists. BMJ. 1998;317(7166):1151-1160. DOI: https://doi.org/10.1136/bmj.317.7166.1151 PMid:9784463 PMCid:PMC1114120

Khamis HJ. An application of Bayes' rule to diagnostic test evaluation. J Diagn Med Sonogr. 1990;6(4):212-218. DOI: https://doi.org/10.1177/875647939000600403

Johnson KM. Using Bayes' rule in diagnostic testing: a graphical explanation. Diagnosis. 2017;4(3):159-167. DOI: https://doi.org/10.1515/dx-2017-0011

National AIDS Control Organisation. Sankalak: Status of National AIDS Response - Fifth Edition. New Delhi: NACO; 2023. Available from: https://naco.gov.in/sites/default/files/Sankalak%20Booklet.pdf [Accessed Apr 1st, 2025]

Kozieł A, Domański I, Szymczak A, Dudzik T, Knysz B, Szetela B. HIV self-testing: a discussion on the benefits, limitations, and implications for public health with a focus on Poland. Diagnostics (Basel). 2024;14(22):2475. DOI: https://doi.org/10.3390/diagnostics14222475 PMid:39594141 PMCid:PMC11593223

Brown AN, Djimeu EW, Cameron DB. A review of the evidence of harm from self-tests. AIDS Behav. 2014;18(Suppl 4):S445-S449. DOI: https://doi.org/10.1007/s10461-014-0831-y PMid:24989129 PMCid:PMC4094790

Zeleke EA, Stephens J, Gesesew HA, et al. Acceptability and use of HIV self-testing among young people in sub-Saharan Africa: a mixed methods systematic review. BMC Prim Care. 2024;25:369. DOI: https://doi.org/10.1186/s12875-024-02612-0 PMid:39407123

Rainer C, Chihota B, Dziva Chikwari C, McHugh G, Dauya E, Mujuru H, et al. Adolescents' and caregivers' perceptions of caregiver-provided testing and HIV self-testing using oral mucosal transudate tests in Zimbabwe: a short report. AIDS Care. 2021;33(1):109-113. DOI: https://doi.org/10.1080/09540121.2020.1749226 PMid:32295406

Matovu JKB, Nambuusi A, Nakabirye S, Wanyenze RK, Serwadda D. Formative research to inform the development of a peer-led HIV self-testing intervention to improve HIV testing uptake and linkage to HIV care among adolescents, young people and adult men in Kasensero fishing community, Rakai, Uganda: a qualitative study. BMC Public Health. 2020;20:1582. DOI: https://doi.org/10.1186/s12889-020-09714-1 PMid:33081735 PMCid:PMC7576713

Rao A, Pachuau HZ, Panda S, et al. Feasibility of HIV self-test implementation among Mizo youths: a field investigation from Northeast India bordering Myanmar. Front Public Health. 2025;13:1408990. DOI: https://doi.org/10.3389/fpubh.2025.1408990 PMid:39975783 PMCid:PMC11835815