For the purposes of the calculations in this report, the committee estimated that there are approximately 23,000 new cases of mycobacterium tuberculosis (TB) in the United States each year. It was assumed that incidence of TB infection increases with age. It is assumed that half the cases occur in people belonging to a high-risk group and half occur in people in multi-drug resistant areas. It was estimated that there are approximately 1,500 deaths associated with TB annually. See Table A16–1.
For the purposes of the calculation in this report, the committee assumed that most cases of TB infection result in pulmonary disease. Extrapulmonary disease is seen in the remaining 12% of infected people. The health utility index (HUI) was assumed to range from 1.0 for treatment of asymptomatic people (described below) to .89 for the 9-month treatment phase for pulmonary TB and .72 for 20 days of severe extrapulmonary TB (including hospitalization). See Table A16–2.
Table 16–3 summarizes the health care costs incurred by TB infections. For the purposes of the calculations in this report, it was assumed that costs are incurred for both active and asymptomatic (suspected and latent) cases of TB. It is assumed that for every case of confirmed, active TB disease, treatment for 3 to 5 asymptomatic (suspected or latent) cases of TB is required until TB infection is confirmed. Asymptomatic, latent infections require additional treatment. These treatments are assumed to include two visits to a general physician, three visits to a nurse, diagnostic evaluation, and medications. Although the model assumes that all suspected cases of TB undergo the care described above, it is assumed that adherence to a 6-month treatment regime for latent infections is not complete (e.g., that 40% of patients take medications for only 3 months).
Health care costs incurred for pulmonary and extrapulmonary TB are assumed to involve hospitalization followed by 9 months of outpatient treatment. This follow-up involves monthly costs for a physician visit, diagnostic evaluation, and medication.