Introduction
The HIV burden remains concentrated in Southern Africa, with estimated adult prevalence ranging between 10.6% in Malawi and 25.6% in Lesotho in 2018.1 Expanding access to HIV testing services (HTS) and ensuring linkage to prevention or timely antiretroviral therapy initiation for people living with HIV is vital to achieving epidemic control. HIV self-testing (HIVST) is an additional testing modality where an individual collects his or her own oral fluid or blood sample, conducts the test and interprets results. HIVST has increased the uptake and frequency of testing among individuals who would not test otherwise.2 3 The Unitaid-funded Self-Testing AfRica (STAR) Initiative led by Population Services International (PSI) started implementing HIVST delivery models in southern Africa in 2016.4 Many HIVST distribution models were evaluated, including community-based, workplace, public and private sector facility-based primary distribution strategies, and secondary distribution strategies to sexual partners and peers among key populations.5
Community-based models delivering HIVST either at people’s homes or within the community setting with mobile outreach were shown to be a convenient approach for reaching undertested groups such as young people (16–25 years old) and men.6–10 Although community-based approaches are expensive from a provider perspective, they decrease users’ costs in accessing HIV testing, in particular among working men whose time might be more expensive.9 11 12 Following the success demonstrated in the STAR Initiative, the Lesotho Ministry of Health added HIVST to its revised national HTS strategic plan for 2018–2023.13 An analysis of the costs of scaling-up HIVST (increasing the provision of HIVST kits) was needed by country planners to inform the HIVST national scale-up plans and budget in Lesotho. However, there is little guidance or empirical evidence on methods for projecting costs at scale for programming and planning.14 15
Cost functions can be derived from a production function to estimate the total cost of production given a specific output produced. The simplest cost function multiplies a single unit cost by a quantity—the commonly used ‘simple cost multiplier’ (SCM). It is a practical costing method used for high level budgeting.15 Accounting cost functions (ACFs) identify all the cost inputs to a production process (equipment, personnel, etc) over a defined costing period (usually 1 year) and categorise them as fixed, semi-fixed or variable costs in the short run or all variable in the long run.14–17 Econometric cost functions (ECF) do not follow the production process but rather apply statistical inference to predict costs. The challenge of ECF is to reflect the complexity of real-world production process with a mathematical model of inputs and outputs.14 16 In most studies, we do not have the luxury of collecting large amounts of location-specific cost data, and applications of ECF for cost predictions are rare.14 18 In the absence of detailed data, SCM is commonly used.
This study aims to fit an ECF to estimate the cost drivers of the community-based HIVST programmes in Southern Africa using data from Malawi, Zambia, Zimbabwe and South Africa. We then inform the use of ECF to predict costs at scale by comparing ECF models with different level of data requirements. Finally, we assess the validity of our empirical ECF by comparing projected costs with observed costs at scale in Lesotho. We select Lesotho as our case study because we conducted in this country a longitudinal microcosting analysis of HIVST scale-up from a real-world intervention over 2 years of implementation.19