Mycobacterium simiae. Clinical features and follow-up of twenty-four patients.

The charts of twenty-four patients from whom Mycobacterium simiae was isolated from the sputum were reviewed and the patients seen in follow-up examination when possible. They were divided into 3 groups: 2 patients were felt to have had definite infection with M. simiae, 3 were felt to have had probable infection, and 19 showed no evidence of infection during follow-up for as long as 6 yr. All patients in the study had underlying pulmonary abnormalities. The results of PPD skin tests were negative in patients without evidence of tuberculosis. The patients without evidence of M. simiae infection were found to have had negative initial Acid Fast Bacillus smears, fewer sputum cultures positive for M. simiae, and lighter yields from cultures of M. simiae compared with those in the patients with M. simiae infection. We conclude that M. simiae is a nontuberculous mycobacterium capable of causing progressive granulomatous lung infection, but that it may also be identified as a causal isolate from the sputum of susceptible persons. Antituberculosis chemotherapy should not be employed in this latter group.