Modeling time taken for HIV testing and visits in follow-up clinic to uptake test results: an application of extended Cox proportional hazard model

Introduction
Improving human immunodeficiency virus (HIV) testing among most at risk popu­lations (MARP) is one of the first steps to achieve sustainable development goal target of ending acquired immunodeficiency syndrome (AIDS) by 2030. Studying the time taken for HIV testing and subsequent clinic visits to collect the results provide important inputs for development of HIV prevention programs. This study aimed to identify the pattern of HIV testing behavior of female sex workers (FSWs) over time and developing of statistical models to describe HIV testing behavior among MARP.

Material and methods
HIV testing data of 5,667 FSWs registered with national HIV prevention program in 10 districts of Sri Lanka during 2016 and 2017 were analyzed using Cox proportional hazard model (CPHM) with time-dependent covariates.

Results
Time taken to acceptance of HIV testing is more dependent on individual factors of FSWs, whereas the uptake of results is less dependent on individual factors. Youth FSWs take more time to accept an HIV test. FSWs who operate in districts out of Colombo, use condoms and report undergoing HIV testing before joining the programme take more time for testing and collection of the results. FSWs with high partner exchange rate (therefore, at high-risk) are less likely to complete both events and take more time for testing. Most of these covariates were identified as time-dependent, and the effects showed a reducing pattern over time. Extended CPHM paved the way to model such variables.

Conclusions
Factors identified in the study, as associated with time taken for both events, can be consider in planning activities leading to HIV preventions programs. Extended CPHM was found to be an alternative technique to CPHM to model time for testing and subsequent clinic visit to uptake the results, especially in the presence of an HIV prevention program.