Modelling the cost-effectiveness of mass screening and treatment for reducing Plasmodium falciparum malaria burden

Abstract

Background: Past experience and modelling suggest that, in most cases, mass treatment strategies are not likely to succeed in interrupting Plasmodium falciparum malaria transmission. However, this does not preclude their use to reduce disease burden. Mass screening and treatment (MSAT) is preferred to mass drug administration (MDA), as the latter involves massive over-use of drugs. This paper reports simulations of the incremental cost-effectiveness of well-conducted MSAT campaigns as a strategy for P. falciparum malaria disease-burden reduction in settings with varying receptivity (ability of the combined vector population in a setting to transmit disease) and access to case management.

Methods: MSAT incremental cost-effectiveness ratios (ICERs) were estimated in different sub-Saharan African settings using simulation models of the dynamics of malaria and a literature-based MSAT cost estimate. Imported infections were simulated at a rate of two per 1,000 population per annum. These estimates were compared to the ICERs of scaling up case management or insecticide-treated net (ITN) coverage in each baseline health system, in the absence of MSAT.

Results: MSAT averted most episodes, and resulted in the lowest ICERs, in settings with a moderate level of disease burden. At a low pre-intervention entomological inoculation rate (EIR) of two infectious bites per adult per annum (IBPAPA) MSAT was never more cost-effective than scaling up ITNs or case management coverage. However, at pre-intervention entomological inoculation rates (EIRs) of 20 and 50 IBPAPA and ITN coverage levels of 40 or 60%, respectively, the ICER of MSAT was similar to that of scaling up ITN coverage further.

Conclusions: In all the transmission settings considered, achieving a minimal level of ITN coverage is a "best buy". At low transmission, MSAT probably is not worth considering. Instead, MSAT may be suitable at medium to high levels of transmission and at moderate ITN coverage. If undertaken as a burden-reducing intervention, MSAT should be continued indefinitely and should complement, not replace, case management and vector control interventions.

Figure 1

Median all-age parasite prevalence over the simulation period. MSAT was conducted annually one month before the trough of transmission in years 5–12, at a pre-intervention EIR of 20 IBPAPA, case management coverage of 20%, two imported infections per 1,000 population per annum, and ITN coverage of 40%. Circles indicate ITN distributions and arrows indicate MSAT campaigns.

Figure 2

Number of episodes averted as a function of number of episodes in the comparator scenario. Number of episodes averted per 1,000 population per year over the eight years of the MSAT campaigns are plotted against the number of episodes in the comparator scenario over the same time period, for each factorial combination averaged over 10 unique seeds. Colours indicate levels of case management coverage: Yellow: 0%, Pink: 20%, Blue: 35%, Black: 55%. Plotting characters indicate levels of ITN coverage: Squares: 0%, Stars: 40%, Circles: 60%, Triangles: 80%.

Figure 3

Logarithm of MSAT ICER as a function of number of episodes in the comparator scenario. Costs and effects were discounted at an annual rate of 3% and aggregated over the eight years of the MSAT campaigns, using the US$7 MSAT cost estimate. The natural logarithm of the MSAT ICER was plotted against the number of episodes in the comparator scenario over the same time period, for each factorial combination averaged over 10 unique seeds. Colours indicate levels of case management coverage: Yellow: 0%, Pink: 20%, Blue: 35%, Black: 55%. Plotting characters indicate levels of ITN coverage: Squares: 0%, Stars: 40%, Circles: 60%, Triangles: 80%.

Figure 4

Logarithm of MSAT ICER in each year of the intervention. The natural logarithm of the annual MSAT ICER was calculated using the US$7 MSAT cost estimate and averaged over 10 unique seeds, in different transmission and health system settings. Lines indicate levels of case management coverage: Yellow: 0%, Pink: 20%, Blue: 35%, Black: 55%.