Costs and consequences of additional chest x-ray in a tuberculosis prevention program in Botswana

Abstract

Rationale: Isoniazid preventive therapy is effective in reducing the risk of tuberculosis (TB) in persons living with HIV (PLWH); however, screening must exclude TB disease before initiating therapy. Symptom screening alone may be insufficient to exclude TB disease in PLWH because some PLWH with TB disease have no symptoms. The addition of chest radiography (CXR) may improve disease detection.

Objectives: The objective of the present analysis was to compare the costs and effects of the addition of CXR to the symptom screening process against the costs and effects of symptom screening alone.

Methods: Using data from Botswana, a decision analytic model was used to compare a "Symptom only" policy against a "Symptom+CXR" policy. The outcomes of interest were cost, death, and isoniazid- and multidrug-resistant TB in a hypothetical cohort of 10,000 PLWH.

Measurements and main results: The Symptom+CXR policy prevented 16 isoniazid- and 0.3 multidrug-resistant TB cases; however, because of attrition from the screening process, there were 98 excess cases of TB, 15 excess deaths, and an additional cost of U.S. $127,100. The Symptom+CXR policy reduced deaths only if attrition was close to zero; however, to eliminate attrition the cost would be U.S. $2.8 million per death averted. These findings did not change in best- and worst-case scenario analyses.

Conclusions: In Botswana, a policy with symptom screening only preceding isoniazid-preventive therapy initiation prevents more TB and TB-related deaths, and uses fewer resources, than a policy that uses both CXR and symptom screening.

Figure 1.

Tornado diagram showing the change in the number of incremental deaths in a cohort of 10,000 persons living with HIV (PLWH), using the “Symptom+CXR” policy versus the “Symptom” policy, through variation of the model parameters. Parameters are ordered from top to bottom by their impact on model outcome. Dark bars represent the upper limit and lighter bars the lower limit of the parameter value. The base-case value is shown in parentheses and 14.5 deaths represents the base-case comparison of the two policies, that is, there are 14.5 more deaths with the “Symptom+CXR” policy than the “Symptom” policy. The “Symptom+CXR” policy reduces deaths only when the attrition is near 0%. CXR = chest radiograph; INH-R = isoniazid-resistant TB disease; IPT = isoniazid preventive therapy; MDR = multidrug-resistant tuberculosis disease; TB = tuberculosis; Timeframe = post-IPT TB-free survival.

Figure 2.

Tornado diagram showing the change in the incremental cost–effectiveness ratio (ICER) of the “Symptom+CXR+Tracking” policy (0% attrition) compared with the “Symptom” policy, expressed in millions of U.S. dollars per death averted in a cohort of 10,0000 HIV-infected adults. Model parameters were varied as shown in Table 1 and cost parameters were varied from 75 to 125% of the base-case values shown in Table 2. Parameters are ordered from top to bottom by their impact on model outcome. Dark bars represent the upper limits and lighter bars the lower limits of the parameter value. The base-case values are shown in parentheses on the left and $2.8 million per death averted is the base-case ICER of the “Symptom+CXR+Tracking” policy compared with the “Symptom” only policy for a cohort of 10,000 HIV-infected adults. Not shown is the incremental cost–effectiveness ratio of using the lower limit for the mortality of isoniazid-resistant TB (10%) or the upper limit for the mortality of background resistant TB (25%), because in these cases the “Symptom+CXR” policy is dominated by the “Symptom” policy (the latter has fewer deaths and is less costly). CXR = chest radiograph; DOTS = directly observed therapy for TB disease; INH-R = isoniazid-resistant TB disease; IPT = isoniazid preventive therapy; MDR = multidrug-resistant tuberculosis disease; TB = tuberculosis.

Figure 3.

Tornado diagram showing the change in the incremental cost–effectiveness ratio of the “Symptom+CXR+Tracking” policy (0% attrition) compared with the “Symptom” policy, expressed in millions of U.S. dollars per new case of isoniazid-resistant TB averted in a cohort of 10,000 HIV-infected adults. Model parameters were varied as shown in Table 1 and cost parameters were varied from 75 to 125% of the base-case values shown in Table 2. Parameters are ordered from top to bottom by their impact on model outcome. Dark bars represent the upper limits and lighter bars the lower limits of the parameter value. The base-case values are shown in parentheses on the left and $14,400 represents the base-case ICER of adding CXR and Tracking per isoniazid-resistant case of TB averted in a cohort of 10,000 HIV-infected adults screened. CXR = chest radiograph; DOTS = directly observed therapy for TB disease; INH-R = isoniazid-resistant TB disease; IPT = isoniazid preventive therapy; MDR = multidrug-resistant tuberculosis disease; TB = tuberculosis.