Research Article

The Costs and Cost-Effectiveness of Mass Treatment for Intestinal Nematode Worm Infections Using Different Treatment Thresholds

  • Andrew Hall mail,

    Affiliation: Centre for Public Health Nutrition, University of Westminster, London, United Kingdom

  • Sue Horton,

    Affiliation: Micronutrient Initiative and School of Business & Economics, Wilfrid Laurier University, Waterloo, Ontario, Canada

  • Nilanthi de Silva

    Affiliation: Department of Parasitology, Faculty of Medicine, University of Kelaniya, Ragama, Sri Lanka

  • Published: March 31, 2009
  • DOI: 10.1371/journal.pntd.0000402

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Cost effectiveness is not the only criterion

Posted by montresor on 23 Apr 2009 at 15:28 GMT

The paper by Andrew Hall et al. provides an interesting point of view into the economic aspects of soil-transmitted helminth control interventions. However, we strongly disagree with the conclusion brought forward by the authors:
We do not think that cost effectiveness is the only criterion to evaluate this kind of intervention:
In fact, the higher the threshold used to trigger treatment, the more cost-effective is the intervention, (because the number of non-infected individuals that receive treatment decreases inversely).
The most cost-effective of any threshold is therefore 100% of children infected, the adoption of any threshold below 100% is the result of a discretionary decision, based on the judgement not only of the cost-effectiveness but taking into consideration the cost-effectiveness of other competing interventions and ethical principles.
In fact, the WHO threshold were developed with the aim of ensuring an adequate treatment to the highest possible number of individuals in need, within reasonable cost limits. There are no doubts that the benefits of anthelminthic treatment are most significant in high endemic areas; however WHO considers that also the smaller health benefits that individuals living in low-endemic areas might still enjoy, need attention because of the overall very low cost of the intervention: treating such areas might have a lower cost-effectiveness, but its low cost still makes it a sound public health intervention.

In addition, we believe that the cost-effectiveness of STH control interventions implemented as per WHO guidelines might be higher than estimated by Hall and colleagues, because of the two considerations below:

On effectiveness
The effectiveness of any STH disease control intervention is likely to be higher than that estimated by Hall et al. for any given prevalence of infection because of the low sensitivity of the diagnostic test recommended by WHO for assessment of prevalence of infection at community level. The Kato-Katz method is known to underestimate the true prevalence of infection by at least about 20% (Knopp et al., 2008): this means that when we detect a community where prevalence is 20%, in reality we know that the prevalence will be about 25%, and so on. As a consequence, at individual level, intensity of infection is also likely to be higher than expected, and the health benefit resulting from treatment will be equally bigger.

On cost
We also believe that the cost of delivering anthelminthic drugs is lower than that calculated by Hall and colleagues for the two following reasons:
1. WHO recommends "integration" of all helminth control interventions into other existing public health interventions. This is particularly true in STH control: as a matter of fact, distribution of ALB/MBD is frequently included in other existing programmes, so that in the end delivery costs are significantly reduced and the only additional cost is limited to the drug itself. For example, vitamin A distribution campaigns cover all under 5s (preschool-age children) in almost every developing country throughout the world, and almost invariably co-administer ALB or MBD to the same target population. In the domain of helminth-only interventions, LF elimination campaigns already target all individuals over 2 years or over 5 years (according to the area) with ALB+IVM or ALB+DEC, thus equally protecting children from STH infections. Hall's calculation are therefore correct when applied to programmes specifically designed and implemented to control STH, which of course exist, but are only one of the possible delivery channels.
2. Calculations made by Hall and colleagues are based on the assumption that the entire National territory is considered as the implementation unit (the geographical area in which the same strategy is applied), while WHO rather recommends the sub-national level (ecological area or region). Choosing a smaller implementation unit is likely to decrease implementation costs by limiting wastage of resources in areas where the disease is not transmitted or does not require implementation of preventive chemotherapy interventions.

In conclusion, for the reasons exposed above, the health benefits of disease control interventions as recommended by WHO are expected to be higher than those calculated by Hall and colleagues for any given threshold of prevalence, while absolute implementation costs are likely to be lower. As a consequence of these two considerations, we believe that the cost-effectiveness of implementing STH preventive chemotherapy following WHO thresholds is higher than that estimated by Hall and colleagues.
It is therefore our opinion that the overall low cost of the intervention, the non-negligible impact on health, united to a sound classification of endemic areas at sub-country level, justify keeping the minimal threshold for inclusion low (20%), so as to provide the largest number of infected individuals with an adequate treatment, and therefore comply with ethical concerns.

A. Montresor and A Gabrielli
Neglected Tropical Diseases
WHO Geneva


Knopp S, Mgeni AF, Khamis IS, Steinmann P, Stothard JR, Rollinson D, Marti H, Utzinger J (2008). Diagnosis of soil-transmitted helminths in the era of preventive chemotherapy: effect of multiple stool sampling and use of different diagnostic techniques. PLoS Negl Trop Dis 2: e33

No competing interests declared.