Cost-Effectiveness Analysis of Interventions
Classifying Interventions
The three major interventions are anthelmintic drug treatment, sanitation, and health education.
Anthelmintic Drug Treatment
Anthelmintic drug treatment ("deworming") is aimed at reducing morbidity by decreasing the worm burden. Repeated chemotherapy at regular intervals (periodic deworming) in high-risk groups can ensure that the levels of infection are kept below those associated with morbidity (figure 24.2) and will frequently result in immediate improvement in child health and development. Anthelmintic drug treatment can prevent the development of irreversible consequences of schistosomiasis in adulthood. For ascariasis and trichuriasis, for which intensity peaks among school-age children, frequent and periodic deworming may reduce transmission over time. Obstacles that diminish the effectiveness of periodic deworming are the low efficacy of single-dose mebendazole and albendazole for the treatment of hookworm and trichuriasis, respectively (Adams and others 2004; Albonico and others 1994); high rates of posttreatment reinfection for STHs in areas of high endemicity (Albonico and others 1995); and diminished efficacy with frequent and repeated use (Albonico and others 2003), possibly because of anthelmintic resistance (see the section "Research and Development").
[Figure
24.2]
Improved Sanitation
Improved sanitation is aimed at controlling transmission by reducing soil and water contamina tion. Sanitation is the only definitive intervention to eliminate STH infections, but to be effective it should cover a high percentage of the population. Therefore, because of the high costs involved, implementing this strategy is difficult where resources are limited (Asaolu and Ofoezie 2003). Moreover, when used as the primary means of control, it can take years or even decades for sanitation to be effective (Brooker, Bethony, and Hotez 2004).
Health Education
Health education is aimed at reducing transmission and reinfection by encouraging healthy behaviors. For STH infections and schistosomiasis, the aim is to reduce contamination of soil and water by promoting the use of latrines and hygienic behavior. Without a change in defecation habits, periodic deworming cannot attain a stable reduction in transmission. Health education can be provided simply and economically and presents no contraindications or risks. Furthermore, its benefits go beyond the control of helminth infections. In this perspective, it is reasonable to include this component in all helminth control programs.
Other Control Measures
In specific epidemiological conditions, environmental or chemical control of snails can be useful tools for reducing the transmission of schistosomiasis. Research to develop new tools for control is in progress, including vaccine development programs for hookworm infection and schistosomiasis (see "Research and Development").
Choosing Interventions
Periodic deworming stands out as the most cost-effective means to reduce the morbidity of STH and schistosome infections.
Periodic Anthelmintic Therapy
Periodic anthelmintic therapy, or periodic deworming, represents the main measure in areas where infections are intensely transmitted, resources for disease control are limited, and funding for sanitation is lacking. Drug treatment can be administered in the community using different strategies:
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Universal treatment. The entire community is treated, irrespective of age, sex, infection status, and other characteristics.
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Targeted treatment. Treatment targets population groups, which may be defined by age, sex, or other social characteristics, irrespective of the infectious status.
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Selective treatment. Treatment targets individual-level application of anthelmintic drugs, which is selected on the basis of either diagnosis or a suspicion of current infection.
Recommended drugs for use in public health interventions to control STH infection are the benzimidazole anthelmintics (BZAs), albendazole (single dose: 400 mg, reduced to 200 mg for children between 12 and 24 months), or mebendazole (single dose: 500 mg), as well as levamisole or pyrantel pamoate (WHO 2002). Praziquantel (PZQ) (single dose: 40-60 mg/kg) is the major drug used for the treatment of schistosomiasis. However, therapy with oxamniquine has been the cornerstone for treatment of S. mansoni infection in South American national control programs over the past 20 years. The efficacy of oxamniquine and PZQ is comparable, although that of PZQ is slightly better. The BZAs and PZQ are inexpensive; they have undergone extensive safety testing and have been used by millions of individuals with only a few minor side effects. Drugs that do not need dosage according to weight, such as BZAs (in school-age children), are considered easier to use for population-based interventions; however, the use of proxy indicators—for example, substituting height for weight—has proved a successful implementation strategy for PZQ (Hall and others 1999).
Distribution Strategy and Frequency of Treatment
The selection of the distribution strategy and the frequency of treatment is based on epidemiological data. The recommended strategy for helminth control is a population-based approach, in which individuals in targeted communities are treated irrespective of their infection status (WHO 2002). This strategy is justified for several reasons, including the simplicity and safety of delivering treatment. Individual diagnosis is difficult and expensive and offers no safety benefit.
The intrinsic transmission potential of the parasite species determines the frequency of treatment (see "Epidemiology of STH Infections and Schistosomiasis," earlier in this chapter). To control morbidity in areas of intense transmission (prevalence greater than 70 percent and more than 10 percent of moderate-and heavy-intensity infection), WHO (2002) recommends treatment two or three times a year for STH infections. In areas with a lower intensity of transmission (prevalence between 40 and 60 percent and less than 10 percent of moderate- and heavy-intensity infection), intervention once a year is recommended (WHO 2002).
School-Age Children as a High-Risk Population
School-age children typically have the highest intensity of worm infection of any age group, and chronic infection negatively affects all aspects of children's health, nutrition, cognitive development, learning, and educational access and achievement (World Bank 2003). Regular deworming can cost-effectively reverse and prevent much of this morbidity. Furthermore, schools offer a readily available, extensive, and sustained infrastructure with a skilled workforce that is in close contact with the community. With support from the local health system, teachers can deliver the drugs safely. Teachers need only a few hours of training to understand the rationale for deworming and to learn how to give out the pills and keep a record of their distribution. School-based deworming also has major externalities for untreated children and the whole community. By reducing transmission in the community of Ascaris and Trichuris infections, deworming substantially improves the health and school participation of both treated and untreated children, both in treatment schools and in neighboring schools (Bundy and others 1990; Miguel and Kremers 2003).
These observations provided a basis for the adoption of resolution 54.19 at the 2001 World Health Assembly, which urged member states to ensure access to essential drugs for STH and schistosome infections in endemic areas for the treatment of clinical cases and groups at high risk for morbidity (box 24.1). To achieve this goal, WHO has developed a broad partnership that promotes the incorporation of deworming into existing institutions and programs, for both the education sectors and the health sectors. The Partnership for Parasite Control was launched in 2001 with the aim of mobilizing resources and promoting synergy among public and private efforts for the control of soil-transmitted helminths and schistosomiasis at global and national levels. School-based deworming has its full effect when delivered within an integrated school health program that includes elements of the Focusing Resources on Effective School Health (FRESH) framework.
[Box 24.1]
Other At-Risk Populations
Not only school-age children can benefit from treatment. Preschool children (one to five years of age) are vulnerable to the developmental and behavioral deficits caused by iron deficiency anemia, and recent analyses by Brooker, Bethony, and Hotez (2004) indicate that hookworm is an important contributor to anemia in that age group (see "Estimating Intervention Effectiveness"). Women of reproductive age (15 to 49 years of age) are particularly susceptible to iron deficiency anemia because of iron loss during menstruation and because of increased needs during pregnancy (Bundy, Chan, and Savioli 1995). In certain circumstances, male worker populations can also be at increased risk (Guyatt 2000).
Estimating Intervention Effectiveness
The evidence base for the health and educational effect of periodic deworming has accumulated significantly over the past decade.
STH Infections
All the anthelmintic drugs mentioned above substantially reduce the number of adult worms in the gastrointestinal tract. This effect is also reflected in reduced fecal egg counts. In some cases, however, the efficacy of single-dose mebendazole or albendazole on hookworm and Trichuris infections is low (Adams and others 2004; Albonico and others 1994). Moreover, pyrantel pamoate has little effect on T. trichiura. Overall, however, anthelmintic treatment significantly improves physical and cognitive outcomes in the following ways:
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Preschool children. Periodic distribution of anthelmintics has a positive effect on motor and language development and reduces malnutrition in very young children (Stoltzfus and others 2004).
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School-age children. Treating school-age children has a considerable effect on their nutritional status (Stoltzfus and others 2004), anemia, physical fitness, appetite, growth (Stephenson, Latham, and Ottesen 2000), and intellectual development (Drake and others 2000).
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Women of reproductive age. Studies of pregnant women conducted by Christian, Khatry, and West (2004) in Nepal indicate that albendazole treatment improves maternal hemoglobin as well as birth-weight and child survival.
Schistosomiasis
As with STH infections, anthelmintic chemotherapy for schistosomiasis has an important effect on child development, growth, and physical fitness (WHO 2002). Richter (2003) recently summarized details of the effect of PZQ on organ pathology. In S. haematobium infections, reversal of urinary tract pathology can be seen six months after a cure. In S. mansoni and S. japonicum infections, much of the intestinal pathology regresses after chemotherapy. However, more than one PZQ treatment is usually necessary to reverse hepatic pathology, especially in areas of intense transmission. Early intervention with PZQ is preferable to reverse organ pathology.
Intervention Costs
Several studies have evaluated the costs of school-based periodic deworming in several different settings, whereas comparable studies on other interventions are still lacking.
Periodic Deworming
The advantage of periodic deworming lies in its simplicity (one tablet per child) and safety. Teachers and other personnel without medical training can easily apply the simple measures, which can be incorporated without difficulty in existing health and nonhealth activities that reach the high-risk group. Several organizations, including nongovernmental organizations, include an STH and schistosome infection-control package within their routine activities and, with very limited budgets, relieve the burden of helminth infections in the population covered. The costs of albendazole and PZQ are available through the International Drug Price Indicator Guide (http://www.msh.org). Delivery systems for deworming have often depended on vertical programs, in which mobile teams visit schools or communities to carry out treatment (WHO 2002). Estimated costs for this approach are outlined in table 24.2. For STH infections in Tanzania, Nigeria, and Montserrat, the costs range from US$0.21 to US$0.51 per treatment. However, by training teachers and other school officials to administer anthelmintic drugs, the system could achieve low-cost delivery by "piggy-backing" on existing programs in the educational sector (WHO 2002). Specific examples of such programs conducted in Ghana and Tanzania are summarized in the section "Implementation of Control Strategies: Lessons of Experience," later in this chapter. It was found that delivery of school-based targeted anthelmintic treatment could cost as little as US$0.03 per child, which may be as low as one-tenth of the estimated costs for vertical delivery (WHO 2002). Thus, at current drug prices, the total cost (drug plus delivery) of a single treatment with albendazole or mebendazole may be as low as US$0.05, and that of a combined treatment with PZQ may be as low as US$0.25 per child (WHO 2002).
[Table .]
Integrating drug distribution through the school system rather than using mobile teams, along with a marked decline in the price of BZAs and PZQ, has resulted in a 10-fold reduction in delivery costs. However, those costs are artificially low because they do not include the external costs for the coordinating center responsible for supporting those approaches (Guyatt 2003). It has been estimated, for instance, that mass albendazole treatment of school-age children in Kenya could cost more than US$3 million each year, equivalent to some 4 percent of current national public expenditure on health care (Guyatt 2003). This analysis has not been evaluated against actual operations, however, and current estimates from the parasite control authorities in Kenya suggest that the actual cost is likely to be far less. Large-scale chemotherapy programs for helminth control continue to rely heavily on donor support, suggesting that some affected countries may be unable to support the costs of deworming.
Monitoring of control programs is an important part of the managerial process, and it should be carried out at minimum cost so as not to divert resources from the intervention (Brooker and others 2004). It is recommended that, at the planning stage, approximately 5 to 10 percent of the program budget be reserved for monitoring activities (Montresor and others 2002).
Improved Sanitation
When sanitation improvements are made alongside deworming, the results obtained last longer. However, the investment needed to reach the level required to interfere with STH transmission could be high. To correctly evaluate the advantage of such investments, one must take into account the consequences for other health indicators and for economic development. An efficient sanitation infrastructure removes the underlying cause of most poverty-related communicable diseases and can boost the economic development of a country. The resources needed to improve hygienic standards can be huge and require the cooperation of several sectors of society (Asaolu and Ofoezie 2003). Currently, these are qualitative judgments, and no cost-effectiveness analysis (CEA) estimates exist for sanitation in this context.
Health Education and Communication
Measures to increase the health awareness of the population are included as an essential component of any population-based activity aimed at controlling morbidity attributable to helminth infections. However, the effectiveness of those activities in reducing transmission of infection varies according to different reports. In some cases, health education can decrease costs, increase levels of knowledge, and decrease reinfection rates (Lansdown and others 2002). Health education efforts can build trust and engage communities, aspects that are crucial to the success of public health initiatives. No CEA estimates exist for health education in this context.
Linking Costs and Effects of Interventions
Interventions to reduce morbidity from helminth infections fall into two categories: targeting the transmission mechanisms and treating individuals directly. The former encompasses improvements in infrastructure, including water supply and sanitation, and health education. The latter entails the periodic drug treatment of the population. Substantial improvements through prevention may be a long-term outcome of economic growth in general, because wealthier households have improved sanitation facilities and practices, but those improvements are not an option in the short term without large investments in infrastructure. As shown in the previous section, deworming options dominate on both effectiveness and cost-effectiveness criteria. Costs continue to fall as drug costs decrease. With better data and detailed mapping of disease distribution within communities, targeting individuals at high risk becomes more feasible, thus improving the cost-effectiveness of control programs (Michaud, Gordon, and Reich 2003).
Evidence from existing programs that narrow the intervention to school-age children (a high-risk group) shows that the treatment costs of chemotherapy for helminth infections are quite low—well below US$1 per school-age child. This finding is in part due to the accessibility of the target group and the cost savings of incorporating delivery into existing school and health programs. Moreover, as discussed in the following sections, the economic benefits of targeting this group may be substantial. Still other targeted groups may also have low cost per treatment when treatment is merged into existing programs. For example, interventions through prenatal care programs for pregnant women may be cost-effective. Likewise, evidence on costs of treatment through existing integrated management of infant and childhood illness (IMCI) programs for small children and health campaigns (such as vaccination and micronutrient programs) find low cost per case treated (Montresor and others 2002).
Several factors can potentially alter the ranking of interventions in regard to cost-effectiveness, although there are no existing studies to evaluate this. Previous analysis may underestimate the effectiveness and overestimate the cost-benefit ratios of mass treatment of school-age children if the externalities of treatment are not considered (Miguel and Kremer 2003). The cost-effectiveness of school-based deworming programs will change as the programs are extended to cover children who are not enrolled in school. Such program extensions are likely to have greater costs because they entail additional staff and outreach efforts per case treated. However, the effectiveness of mass treatment of school-age children (both enrolled and not enrolled) may be greater. Children who are not enrolled in school come from households with lower income levels. Lower income, which leads to poorer sanitation conditions, is associated with greater incidence and intensity of infections. Expanding mass treatment to children not enrolled in school will result in treating populations that have higher incidence and intensity, thus raising effectiveness (box 24.2).
[Box 24.2]
Distributional and Equity Consequences
Interventions to control helminth infections can have equity implications in several dimensions. Programs designed to target communities with high prevalence or high intensity of helminth infection focus on areas with lower income, as described in the sections on the causes, characteristics, and epidemiology of such infections. Although no studies undertake benefit-incidence analysis of public spending on such health services, this targeting implies that state subsidies on deworming services will be of most benefit to lower-income groups. With the increasing availability of poverty maps, empirical evaluation of the equity implications of deworming will be feasible.
