Population and intervention
The study was conducted in the Rufiji, Kilwa, and Kibiti districts of Tanzania from July 2019 to October 2021. Catchment areas of public and private health facilities within selected wards in these districts were assigned to an intervention or control group. Treatment assignment was non-random, with assignment decisions made based on malaria incidence rates within each catchment area across intervention and control groups [15]. The intervention involved targeted community-based testing of villages with high weekly malaria incidence rates (a “campaign”) using malaria rapid diagnostic tests (mRDTs). Subsequent treatment of those testing positive with dihydroartemisinin piperaquine phosphate (DHA-PPQ) followed the national policy guidelines for malaria treatment [16]. Locally trained community health workers conducted the community-level testing and treatment by setting up temporary testing and treatment stations in the high-burden communities. Additional details on the implementation of the 1,7-mRCTR intervention and the results of the impact evaluation have been published elsewhere [13–15].
Two waves of cross-sectional household surveys were conducted: the first between July and September 2019 and the second between September and October 2021. These surveys assessed malaria prevalence at baseline and endline within the intervention and control groups by using mRDTs to test one randomly selected household member from each of three age groups, if available to be surveyed (under 5, ages 5 to15, and above 15 years). Malaria prevalence was calculated as the total number of positive tests divided by total number of tests performed. The household surveys also incorporated questions on socio-economic characteristics, including household income and costs associated with malaria illness (e.g., lost productive time and fees paid for healthcare services and treatment).
Costing approach
We assessed costs from a societal perspective, which included the costs of delivering the 1,7-mRCTR intervention, the costs or cost-savings resulting from changes in demand for related health services, and the costs or cost-savings experienced by individuals and households due to changes in disease incidence or need for healthcare. We defined health system costs as the 1,7-mRCTR intervention costs plus the costs and cost-savings resulting from changes in provision of routine malaria diagnosis and treatment due to the intervention. Patient costs were defined as the sum of the direct non-medical, productivity, and direct medical costs incurred by patients and their households. Direct non-medical costs represent non-medical expenditures incurred due to illness or to receive care, including food and travel costs incurred while visiting a health facility for malaria testing. Productivity costs represent changes in household economic productivity due to individuals being unwell, or time lost while seeking and/or providing care for sick household members. Direct medical costs represent payments made by patients and their households for medical services and products, including registration and consultation fees, the cost of malaria rapid diagnostic tests, and drug costs [17].
Cost data collection and analysis
We collected cost data using a combination of micro-costing methods for patient costs and macro-costing methods for programmatic costs [18]. The total programmatic costs required to deliver the 1,7-mRCTR intervention were collected during intervention implementation and apportioned into research-related and intervention-related costs. Research-related costs, which are expenses incurred only for the purposes of the study and not expected under routine implementation, were excluded from the analysis. Patient costs were estimated from household survey data collected at baseline and endline. The productivity component of patient costs was calculated by multiplying lost productive time by the average daily income calculated from household survey data.
We assumed that individuals who developed malaria would experience one of three scenarios: they could be diagnosed and treated at a health facility, diagnosed and treated during a 1,7-mRCTR campaign, or remain undiagnosed and untreated for the duration of their illness. The cost of a routine malaria episode diagnosed and treated at a health facility was calculated as the sum of the direct non-medical, productivity, and direct medical costs reported by individuals in household surveys who sought care for malaria symptoms. To calculate the cost of a malaria episode diagnosed and treated during a 1,7-mRCTR campaign, we assumed that an individual testing positive during a 1,7-mRCTR campaign would accrue only one half of the productivity costs due to illness, and not experience lost productive time from healthcare seeking. To calculate the cost borne by an individual with an undiagnosed and untreated episode of uncomplicated malaria, we assumed an individual would lose 3 days of productive time due to illness.
All costs collected in Tanzanian shillings were adjusted for inflation to 2022 values using the GDP deflator for Tanzania [19]. Costs were then converted to US dollars using the 2022 average market exchange rate of 2,329 shillings to 1 US dollar [20]. Future costs were discounted at 3%. All results are reported in 2022 US dollars.
Impact on malaria prevalence and diagnoses
The effect of the 1,7-mRCTR intervention on malaria prevalence was derived from a published impact evaluation that analyzed mRDT positivity from the baseline and endline household surveys [15]. In addition, we used malaria register data from health facilities in intervention and control wards to calculate the total number of passively detected malaria cases over the study period. Data from the 1,7-mRCTR campaigns, including the number of campaigns, tests conducted, and positive mRDTs, were used to calculate the total number of malaria cases diagnosed by reactive case detection in the intervention arm.
Impact on malaria incidence, deaths, and DALYs
We used OpenMalaria, an open-source transmission-dynamic malaria microsimulation model, to simulate malaria epidemiology within the study region and to assess the impact of the 1,7-mRCTR intervention on health outcomes that could not be assessed empirically: malaria cases, deaths, and DALYs [21]. We initialized the model with a population of 10,000 individuals with age distribution based on the Ifakara district of Tanzania [22]. Using the model, we simulated malaria epidemiology from January 2017 to January 2024 using a five-day time step. Discrete-time population models of mosquitoes followed a seasonally forced pattern using a calibrated parameter value for the average annual pre-intervention entomological inoculation rate (EIR) of 4.75 infectious bites per person-year. A burn-in period of one lifespan established a stable level of immunity within the simulated population. The model was fit to malaria prevalence calculated from the baseline household survey and the effect estimate (4.5 percentage point reduction in malaria prevalence) reported by the impact evaluation [15].
We ran 100 simulations for each of two scenarios: one including the 1,7-mRCTR intervention and one without any intervention to represent the counterfactual (i.e. passive detection only) scenario. Each pair of simulations was initialized using the same random seed. In the intervention scenario, individuals could be treated for malaria through two routes: individuals with symptoms could seek care at a health facility or be screened and treated during a campaign. We utilized monthly deployments of mass screen-and-treat campaigns using mRDTs from October 2019 to September 2021 parameterized from trial data, based on the timing and coverage (i.e. proportion of the population screened) of each campaign. To replicate observed interruptions in campaign deployments from the COVID-19 pandemic and mRDT stock-outs, we modelled no campaign deployments from April through May 2020 and in April 2021.
Model outcomes were aggregated from September 2019 (the date of the first 1,7-mRCTR campaign and baseline prevalence measurement) to January 2024 (28 months after the last campaign, the length of time required for malaria incidence to return to pre-intervention levels) to capture longer-term effects of the intervention on malaria incidence and deaths. These outcomes were also used to evaluate the impact of the intervention on malaria deaths and disability adjusted life-years (DALYs). Estimates of years lived with disability (YLDs) per malaria case and years of life lost (YLLs) per malaria death were obtained from the Global Burden of Disease Collaborative Network [23].
Cost-effectiveness analysis
We conducted a cost-effectiveness analysis using empirical cost data and outcomes from the trial for proximal health effects, and modelled estimates of malaria cases, DALYs, and deaths. Cost-effectiveness results are reported as incremental cost-effectiveness ratios (ICERs), which represent the ratio of incremental costs to incremental health benefits for the 1,7-mRCTR intervention compared with the status quo of passive case detection.
We report the results for five cost-effectiveness endpoints: (i) the incremental cost per person treated in a 1,7-mRCTR campaign, (ii) the incremental cost per additional malaria case detected through a combination of passive and reactive case detection, (iii) the incremental cost per incident malaria case averted, (iv) the incremental cost per malaria death averted, and (v) the incremental cost per DALY averted. For the first and second endpoints, incremental costs were defined as the intervention-related programmatic costs. Incremental costs for the third, fourth, and fifth endpoints were defined as the intervention-related programmatic costs plus the cost difference between the intervention and control arms in terms of the costs of malaria diagnoses made at the health facility, costs of diagnoses made in a campaign, and costs associated with undiagnosed and untreated individuals with malaria. This captures the cost savings of reactive case detection through two channels: the reduced burden borne by patients and the health system as individuals are tested and treated in their villages, and lower malaria incidence due to individuals with malaria being identified and treated earlier in the course of illness, which reduces the risk of transmission.
Statistical analysis
We assessed the uncertainty around incremental costs using a non-parametric bootstrap with 10,000 iterations. For incremental effects on malaria incidence, deaths, and DALYs, we used the OpenMalaria simulation results to construct probability distributions describing the additional uncertainty associated with the modelled results. We used a Monte Carlo simulation to combine the different sources of uncertainty, producing a set of 10,000 results representing the overall uncertainty in each outcome of interest. Uncertainty intervals are reported as equal-tailed 95% confidence intervals (CIs), scatterplots on the cost-effectiveness plane, and cost-effectiveness acceptability curves. ICERs were compared to willingness-to-pay thresholds based on the effects of changes in health expenditure in Tanzania on survival and morbidity burdens of disease, using an approach described by Ochalek et al. [24].
Sensitivity analysis
We performed a one-way deterministic sensitivity analysis on key parameters in the analysis, including the intervention-related programmatic cost, duration of illness for undiagnosed and untreated individuals, and the duration of illness before seeking treatment. We varied the intervention-related programmatic cost by ±15% from the base case and the duration of illness by ±1.5 days from the base case.