Cost-Effectiveness of Managing Endemic Tuberculosis
The primary problem in global TB control is the management of disease in countries where incidence has been roughly stable for many years (that is, where TB is endemic).
Cost per Case Prevented
In monetary terms, the cost-effectiveness (C/E) of a new program of treatment for active infectious disease (here defined as sputum-smear positive), per case prevented, can be calculated from C/E P/epsilonkT, where P is the cost of treatment, epsilon is the efficacy of treatment, k is a constant determined by the mode of action of the intervention, and T is the duration of the intervention in years (online annex 5). The cost per case prevented is mostly in the range of US$1,000 to US$10,000, depending on the region of the world (figure 16.1). The exception is Europe and Central Asia, where costs are high because patients are currently treated for long periods in hospitals rather than on an ambulatory basis. These cost-effectiveness ratios (CERs) are computed from the total costs and total effects of treatment. Costs are therefore the same as the incremental costs for new programs. If costs and effects are compared with those of a previous treatment program, CERs for the treatment of active disease are often negative; that is, the program sooner or later saves money, as well as preventing TB cases. The positive CERs reported here for new treatment programs are, in this sense, upper estimates.
[Figure
16.1]
The cost of TLTI per active case prevented also depends on the initial incidence rate (I) and is calculated from C/E P/epsilonkIT (online annex 5). The cost is substantially higher than that for the treatment of active TB: US$20,000 to US$40,000 when radiography is used to exclude patients with active disease, but it is less (US$13,000 to US$20,000) if active TB can be ruled out on the basis of symptoms and clinical examination (figure 16.1). TLTI is less cost effective than the treatment of active TB because preventive treatment would be given to latently infected individuals, most of whom were not recently infected and who are at small risk of developing active disease. In an endemic setting, there is no feasible method of identifying individuals who have recently acquired infection and who will proceed rapidly to active TB.
A new vaccine that prevents infection and, hence, the progression to pulmonary TB among people who were previously uninfected would be extremely competitive (US$90 to US$200) per case prevented if the costs were the same as those for BCG. BCG is cheap to manufacture and administer (US$1 to US$3 per dose) but less cost-effective (US$2,000 to US$8,500 per case prevented) than the treatment of active disease because it is assumed to protect against severe forms of childhood TB only and because it does not affect transmission (figure 16.1).
Cost per Death Prevented and DALY Gained
The wider benefits of treating active TB are revealed when allowing for the additional reduction in case fatality. For a 10-year program of treatment for infectious TB, the cost per death prevented is typically US$150 to US$750, and the cost per DALY gained is US$5 to US$50 for all regions except Europe and Central Asia (figure 16.1). When TB is close to the endemic equilibrium, the extra benefits gained from reducing transmission under DOTS are small: the cost per DALY gained is only 60 percent higher when transmission benefits are excluded. The treatment of noninfectious TB is less cost-effective (US$60 to US$200 per DALY gained), not primarily because transmission is unaffected, but because the case fatality of untreated smear-negative and extrapulmonary disease is relatively low. Treating infectious MDR-TB is between two and ten times more costly than treating drug-susceptible TB per death prevented (greater than US$2,000), or per DALY gained (greater than US$90), assuming resistant bacilli are as transmissible and pathogenic as susceptible bacilli.
BCG vaccination is not much less cost-effective than the treatment of active disease (US$40 to US$170 per DALY gained; higher where the risk of infection is lower). If a new vaccine with 75 percent efficacy against pulmonary disease and other forms of TB costs the same as BCG, it would be almost as cost-effective (US$20 to US$100 per DALY gained) as the ambulatory treatment of active TB. As expected from the preceding analysis, TLTI is much more expensive than all other options (US$5,500 to US$26,000 per DALY gained) and most costly where the death rate from TB among adults is already relatively low—for example, because an effective DOTS program already exists. Although the cost-effectiveness of each intervention varies among regions, the variation among strategies is much greater, whatever the outcome measure (figure 16.1).
