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

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.


Ministry of Health (MOH) personnel. If only supplies, transportation, and lodging for
CHWs were included, the cost was 2006 US$66 per CHW trained. Significantly more trained CHWs conducted and read the test results correctly compared to CHWs who had received only the manufacturer's instructions or job aids [9].

Neglected tropical diseases
Preventive chemotherapy is used as a key approach in control and elimination programmes for neglected tropical diseases (NTDs), notably LF, schistosomiasis, onchocerciasis, soil-transmitted helminths and trachoma [10]. These diseases are often found in areas that are co-endemic for malaria. Many components of MDA programmes against these diseases could be quite similar to those of MSAT programmes against malaria. Therefore, the costing literature for MDA for these NTDs was reviewed, with a focus on African settings. A major difference between the costs of MDA for NTDs and malaria is that drugs for MDA are often donated, and thus incur zero financial costs to the control programme. In addition, distribution often relies on unpaid volunteers, which is also not included in estimates of financial costs.
LF is currently targeted for elimination by the World Health Organization, and the principal strategy relies on concurrent administration of a drug combination, albendazole with diethylcarbamazine (DEC) or albendazole with ivermectin, once-yearly for four to six years. A multi-country cost analysis of MDA for LF published in 2007 revealed that financial costs per person treated per round (not including drugs or volunteer time) in the sub-Saharan African programmes ranged 2002 US$0.06-0.54, with coverage rates ranging 65%-91%. However, when the cost of donated materials, notably drugs, was included, cost per person treated was around US$5 [11].
All of these programmes involved house-to-house visits by volunteers, with or without additional distribution through distribution posts. Cost categories were: training, mapping, mobilization and education, drug distribution, adverse reaction monitoring, surveillance/laboratory (e.g. tracking of community members in MDA area, laboratory work for case identification, testing, etc.), and administration. Input categories were: medications and laboratory supplies, personnel, transport, general supplies, and recurrent and capital costs for facilities and equipment. The analysis was conducted from a national programme perspective and, as many inputs were shared among multiple programmes, costs were apportioned accordingly. Drug distribution generally represented the largest proportion of financial expenditure. The principal determinants underlying variability in the LF costing appeared to be the number of years that the programme had been running; the use of volunteers; and the size of the population treated [11].
Mean financial cost of the African Programme for Onchocerciasis Control was 2008 US$0.58 per person treated, not including volunteer time, which was valued at 2008 US$0.16. Again, drugs were donated so are not included in the cost. The scale and stage of the programme made a large difference to unit costs [12].

MDA for malaria
Only one article with information on the cost of MDA for malaria was found in a literature search. A weekly MDA in Vanuatu, conducted by trained village volunteers for nine weeks (together with ITN distribution and implementation of larvivorous fish), cost US$9 per person: US$5.6 for the impregnated bed nets, US$0.7 for anti-malarials, US$0.4 for materials for microscopical diagnosis, and US$2.3 for transportation and travel allowances for the staff and volunteers. About 90% coverage was achieved in the first three rounds [13]. This MDA was conducted on a small island at short intervals, which is quite different from annual MSAT scenarios in mainland Africa.
Some other studies contained useful information about the operational considerations when undertaking MDA for malaria, such as on how the intervention was carried out, on the number of households that could be visited in a day, and on realistic coverage levels.
For example, a report from an MDA in Tanganyika (present-day Tanzania) described the detailed individual census system that was drawn up before the trial and continually updated, and noted the need for repeated household visits and community participation to achieve high population coverage [1]. One study gave an indication of the time that would be needed to cover a particular population with MDA in an area of north Nigeria with reasonably good accessibility [14]. A report on the Garki project in northern Nigeria stated that in compact villages, each two-person team covered between 150-180 people per day, whereas in scattered villages, they covered around 90-100 persons per day [15].
Of course, these interventions did not involve screening prior to treatment.
Although these costs give a useful indication of what could be expected with MSAT for malaria, the interventions are so different that they cannot be applied directly to MSAT for malaria; screening prior to treatment, as in the case of MSAT for malaria, is a more complex and time-intensive intervention than mass treatment alone and will require additional training of volunteers or CHWs.

Algorithm
The screening cost per person screened ( p S ) in an MSAT campaign round was estimated according to the formula: where p E is the household enumeration cost per person screened, P M is the social mobilization cost per person screened, p D is the delivery cost per person screened, p I is the volunteer or CHW supervision cost per person screened, and p T is the volunteer or CHW training cost per person screened.
For those that test positive and receive a drug, the drug cost needs to be added. These costs will depend on the total prevalence level in the population and the relationship of prevalence to age.

Household enumeration ( p E )
Costs of surveying and conducting a census of the target population were assumed to be borne every time a mass treatment campaign was planned. In reality, costs in subsequent rounds might be lower if only updating of an existing census were required.
Household enumeration costs were borrowed from a study which estimated the perperson cost of conducting a national census in Tanzania [16] (Table A1 and Table 3).

Social mobilization ( P M )
Costs for social mobilization are programme costs, which are relatively fixed irrespective of the covered population size; as such the per-person costs are quite sensitive to the intervention scale. Social mobilization costs were borrowed from a cost study of introducing ACT [17] (Table A1 and Table 3). This study reported the costs of development and production of information, education and communication (IEC) materials and communication and publicity in a rural Tanzanian district of approximately 200,000 population over three years. While the ACT introduction study assumes that the cost of these activities declines in subsequent years, for the MSAT programme, a constant per person cost per round (as in year 1) was assumed, given the more intense communication efforts that would be required with a MSAT programme (owing to the need to achieve high coverage and the fact that the target population is not ill).

Delivery costs ( p D )
Delivery Assumptions made in the calculation of remuneration costs are summarized in Tables A1   and A2 and per-person costs under assumptions 1 and 2 are presented in Table 3.
The cost of supplies per person screened per round, p U , is estimated as where p R is the cost of an RDT, p L is the cost of a lancet, p G is the cost of a pair of gloves, p A is the cost of an alcohol swab, and p Y is the cost of paper and printing per person. Sources for these prices are given in Table A1.
RDT costs were calculated with an additional 12% added for transport, insurance and delivery [18] and another 25% for wastage [19]. For the other supplies, delivery was not costed, but the 25% wastage rate was assumed.
Per-person cost of supplies is presented in Table 3.

Supervision
Cost of supervision per person screened per round, p I , was estimated as Per-person cost of supervision under assumptions 1 and 2 is presented in Table 3.

Training
Training of volunteers or CHWs is needed before each round. In situation 1, the CHWs have already been trained in presumptive management of febrile illness. However, they need to be instructed in the MSAT intervention and trained in conducting and interpreting RDTs and record-keeping. RDT training costs were borrowed from a study in Zambia [9].
In situation 2, where no network of community health workers yet exists, volunteers need to be recruited and trained in all aspects of the intervention (RDT, ACT administration, etc). Recruitment and training costs were borrowed and adjusted from a study of a community health worker strategy in Nigeria [7].
Training costs per person screened per MSAT round for situation 1 are thus estimated as where v N is the total number of CHWs participating in the campaign, pr C is the cost of the RDT training course per CHW, and p N is the number of people screened.
Training costs per person screened per MSAT round for situation 2 are estimated as where v N is the total number of CHWs participating in the campaign, pt C is the cost of recruiting and training per CHW, and p N is the number of people screened.
Training costs per CHW or volunteer are sensitive to the scale of the training programme.
Costs for recruiting and training in situation 2 were modified in an attempt to adjust for this (see Table A1), but this remains a source of uncertainty in our costing estimate.
Sources for training costs are presented in Table A1 and per-person cost of training in situations 1 and 2 and under assumptions 1 and 2 is presented in Table 3.

Artemisinin-based combination therapy
Prices for ACT were as described in a previous publication [18]. Costs were calculated with an additional 12% added for transport, insurance and delivery [18] and another 25% for wastage [19]. ACT costs are presented in Table 3.

Calculation of total costs
The cost estimates are summarized in Table 3. In situation 1, cost per person screened per round is estimated as US$5.08 under assumption 1, and US$6.72 under assumption 2. In situation 2, cost per person screened per round is estimated as US$7.80 under assumption 1, and US$11.08 under assumption 2.

Discussion
To date, MSAT has not been implemented anywhere, so there were no actual costs that could be used for this analysis. However, it is encouraging that the estimate of roughly US$5-11 per person screened (including RDT costs but excluding drug cost) is in a similar range to the cost per person treated in a once-yearly MDA for LF (US$5, including drug cost, no screening) [11]. This analysis suffers from the inevitable limitations of a generic costing based on secondary data. First, the cost of non-tradable inputs (e.g. personnel) could be expected to vary significantly among countries, for example according to level of income [20], which was not considered. Second, this cost estimate included primarily the marginal costs of MSAT, assuming that the health system could accommodate the intervention without, for example, hiring additional staff in health facilities or expanding the drug supply system. The validity of that assumption will depend very much on whether there is spare capacity in the health system. Two situations were considered; one where CHWs were already managing febrile illnesses and another where a system of village volunteers needed to be set up. Since training costs for volunteers or CHWs constitute about a quarter of the total costs of the intervention, this is likely to be a major component of the costs of investing into the health system. As mentioned above, efficiencies of scale or scope that could be achieved by expanding MSAT or integrating MSAT with other disease control programmes were not considered.
However, as the majority of costs are variable, this is unlikely to change the estimate significantly.
It is not clear how the costs of an intervention involving household visits would vary with population density: e.g. the difference between rural and urban settings. Distances between households are shorter in cities so transport and time costs will likely be lower, but it may also be harder to find people at home in large cities than in villages [21] and thus more repeat visits may be necessary in cities. Two different assumptions about the number of household visits that could be accomplished in a day were made in an attempt to account for this. Transport for the village volunteers or CHWs was assumed to be negligible, since they live within the community, but for very spread-out villages these could be more substantial.
More data is needed on the operations and costs of interventions involving household visits in sub-Saharan Africa, as these may be necessary to reach the high levels of intervention coverage called for in global malaria control targets. It is hoped that the work described here contributes to discussions about the costs, feasibility and efficiency of these types of interventions.  Wastage rate of drugs and supplies 25% [20]