Between July 1970 and December 1979, 92 patients with atypical mycobacterial infections of the lung were hospitalized 110 times at Blue Ridge Hospital (Charlottesville, Va). These patients comprised less than 3% of all patients hospitalized for active mycobacterial disease. Sixteen had Mycobacterium kansasii or group I disease, three had group II disease (two M scrofulaceum, one M szulgai), 70 had group III disease (68 Af avium-intracellulare, two M xenopi), and three had M fortuitum or group IV disease. M kansasii infections comprised 23% of the total during the first five years, but only 6% during the second half of the decade. Clinical and roentgenographic findings were similar to those in patients with tuberculosis. As anticipated, most of the M kansasii organisms were sensitive to antimycobacterial drugs, and these patients generally responded well to chemotherapy. In contrast, most of the group III organisms, including one of the M xenopi, exhibited resistance to several drugs. Despite the high incidence of resistance, 59% of the patients with group III infections who were treated for at least three months in the hospital had sputum cultures converted to negative.
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