Summary of Cost-Effectiveness Analyses
Box 16.1 summarizes the results of these calculations of the cost-effectiveness of managing epidemic and endemic TB. The findings are one justification for maintaining and expanding DOTS programs, on the basis of SCC for patients with active disease, as the dominant mode of TB control around the world. BCG vaccination and the treatment of MDR-TB (standard or individualized regimens) or HIV-infected TB patients (with or without supporting antiretroviral therapy) are more costly in absolute terms, but they typically cost less than US$1 per day of healthy life gained, which is less than the average economic productivity of workers in the least developed countries. TLTI appears to be relatively poor value for money, even though this analysis assumes that one course of treatment prevents active TB for life. TLTI is more cost-effective in epidemic than in endemic settings, and it is more cost-effective when it is used to treat individuals coinfected with TB and HIV. A new, high-efficacy vaccine that prevents infection and the progression to pulmonary TB in adults, to be directed at the control of endemic TB, would be more cost-effective than BCG at the same price and almost as cost-effective as SCC.
[Box 16.1]
Averted and Avertable Burden of Tuberculosis
Trends in case notifications can be used, judiciously, to assess regional and global trends in TB incidence, but no satisfactory large-scale analysis has been done of the number of cases prevented by chemotherapy (as distinct from the reductions in transmission and susceptibility associated with improved living standards). One approach to evaluating the averted and avertable burden of TB begins with the observation that 86 percent of the years of healthy life lost that are attributable to TB are from premature death, and only 14 percent are from illness. Because DALYs lost are dominated by premature death, a conservative estimate of the burden of TB alleviated can be obtained in terms of the number of deaths and associated DALYs gained, regionally and globally, since the introduction of the DOTS strategy in 1991.
Figure 16.3 is derived from recent estimates of cases and deaths and their trends by region, including those attributable to HIV coinfection (Corbett and others 2003; WHO 2004c). In the MDG baseline year, 1990, approximately 1.5 million TB deaths (28 per 100,000) occurred. BCG vaccination saved roughly 650,000 deaths from extrapulmonary TB among children between 1990 and 2003. If chemotherapy is assumed to reduce only the case-fatality rate and to have no effect on transmission and incidence, 23 million deaths (44 percent) would have been saved in non-DOTS treatment programs. The expansion to 45 percent case-detection rate under DOTS during the same period saved an estimated 2.3 million (5 percent) additional deaths, the largest numbers in Sub-Saharan Africa (1.1 million), East Asia and the Pacific (558,000), and South Asia (408,000). Further analysis shows that, if 70 percent of TB cases (smear positive and smear negative) can be treated under DOTS before MDG target year 2015, an estimated 1.9 million TB deaths (26 per 100,000) will occur in that year, a greater number than in 1990, but a 7 percent lower death rate per capita (Dye and others 2005).
[Figure
16.3]
The calculations for Africa assume that treatment cures TB in the majority of HIV-infected patients even though, without antiretroviral therapy, many of these patients will die anyway. Despite these favorable assumptions, the number of TB deaths was evidently still rising in Africa in 2003, whereas it was falling in Asia, aided by the large programs of DOTS expansion in China (1991-97) and India (from 1998).
Reducing the TB death rate sufficiently to meet the MDG target requires a significant cut in incidence, as well as in case fatality. An extension of this assessment suggests that case detection must reach at least 70 percent and the TB incidence rate must fall by 5 to 6 percent annually between 2003 and 2015 (Dye and others 2005). For the world, excluding Sub-Saharan Africa and former Soviet republics, the incidence rate would have to fall at a more modest 2 percent per year.
New diagnostics, drugs, and vaccines would also help reduce the global TB burden more quickly. The most desirable of these is a vaccine that prevents pulmonary disease, whether or not vaccination subjects are already infected (a pre- or postexposure vaccine), and that confers lifetime immunity (Andersen 2001; Fordham von Reyn and Vuola 2002; McMurray 2003; Young and Stewart 2002). A new vaccine with high efficacy against pulmonary TB would almost certainly change immunization practice: mass vaccination campaigns among adults (rather than infants) would have dramatic effects, going far beyond the expectations of DOTS programs (figure 16.4; Dye 2000). A postexposure vaccine that stops progression to disease among those already infected, as well as preventing infection in others, would have greater effect than a preexposure vaccine that only prevents infection (Lietman and Blower 2000). However, such calculations are at present highly speculative, because the mode of action and efficacy of any new vaccine is unknown.
[Figure
16.4]
Economic Benefits of Tuberculosis Control
Preventing TB deaths brings no savings in the costs of TB control unless it is accompanied by a reduction in incidence so that fewer patients require treatment. The prompt and effective treatment of active disease is almost certainly reducing transmission around the world, but because the effect on incidence is necessarily slow, it has been hard to quantify in all but a few countries, notably Peru (Suarez and others 2001).
The monetary savings implied by a reduction in incidence of one-quarter (26 percent) between 2000 and 2015—which may be enough to achieve the MDG targets—could be magnified or diminished by adjustments to the DOTS strategy. On the one hand, without compromising cure rates, chemotherapy can be delivered more cheaply to outpatients than inpatients and with less reliance on x-ray diagnosis and surgical procedures. On the other hand, various additions to DOTS—contact tracing, active case finding, antiretroviral therapy for HIV-infected patients, second-line drugs for patients carrying resistant bacilli, or joint public-private schemes for the management of TB—might be desirable but more costly per year of healthy life gained. Whether the savings made by reducing incidence and improving efficiency offset the costs of DOTS add-ons will, therefore, depend on the setting.
Besides the possibility of reducing diagnostic and treatment costs, improved health and longevity yield other economic benefits, but the quantification of those benefits is always controversial. This difficulty is reflected in the limited number of cost-benefit analyses of TB control; among the few examples, one detailed study in India estimated the potential societal benefits of DOTS to be worth US$8.3 billion in 1993-94, or 4 percent of the gross domestic product (Dholakia 1996). Without attempting to extend such analyses here, we note that the preceding results also imply that large-scale treatment programs for TB are likely to give net returns on investment or at least to appear to be good value for money in ways that go beyond the arguments from cost-effectiveness (Jack 2001).
The analysis earlier in this chapter showed that SCC typically costs up to US$30 per DALY gained for the treatment of infectious TB and up to US$200 per DALY gained for the treatment of noninfectious TB (excluding Europe and Central Asia). These figures can be compared with a recent estimate of US$1.5 billion as the annual global cost of treating 70 percent of cases with 85 percent cure (WHO 2004c). Reaching these targets would prevent approximately 2.1 million of all the TB deaths expected if no treatment were available in 2003, including 391,000 deaths prevented by DOTS (figure 16.3). Because each TB death prevented gains approximately 20 DALYs (WHO 2002b), the total cost per DALY gained would be about US$36. This rough calculation excludes any benefits in reduced transmission but includes the costs of treating smear-negative and extrapulmonary TB and is of the same order of magnitude as the results from CEA.
However the calculation is done, the cost of gaining a year of healthy life under DOTS is substantially less than the annual average productivity per capita in the low-income (gross national income [GNI] less than or equal to US$735) or least developed (GNI average US$290, http://www.worldbank.org) countries, and it is probably less than the marginal productivity of labor in the poorest communities. It is also less than twice the average annual income per capita, which has also been proposed as a benchmark for assessing whether an intervention is cost-effective (Garber and Phelps 1997). Moreover, it is less than the World Bank's definition of absolute poverty (living on US$1 per day or less, close to average GNI per capita for the least developed countries) and is certainly less than the monetary values that are typically placed on the value of a human life year (for example, a life was valued at US$100,000 by the 2004 Copenhagen Consensus panel, http://www.copenhagenconsensus.com). All these comparisons suggest not only that the basic DOTS strategy, and perhaps even an enhanced DOTS strategy, are cost-effective but that they also have very favorable cost-benefit ratios.
