Clinical and radiological features of Mycobacterium kansasii infection and Mycobacterium simiae infection

This retrospective study sought to systematically identify clinical and radiological features of Mycobacterium kansasii and Mycobacterium simiae infections. The sample included consecutive patients with a culture-positive diagnosis of M. simiae infection (n=102) or M. kansasii infection (n=62) derived from the databases of the Laboratory of Microbiology of a tertiary medical centre and two outpatient tuberculosis centres. Data on patient background and clinical features were collected, and chest radiographs were analysed. Sixty percent of the M. kansasii group were native born compared to 18% of the M. simiae group (p=0.0001). M. simiae infection was associated with a higher rate of co-morbid disease, including diabetes mellitus, heart disease, and malignancy. A similar rate of lung disease was found in both groups. Clinical symptoms were significantly more common in patients with M. kansasii infection. On radiological study, M. kansasii infection was associated with more cavitations, and M. simiae infection with more pulmonary infiltrates. Patients with M. simiae infection had a higher likelihood of middle and lower lobe disease whereas patients with M. kansasii infection had more upper lobe disease (p=0.001). Pleural effusions and lymphadenopathy were found only in the presence of M. simiae infection. We concluded that there are major differences in the epidemiologic features of M. kansasii and M. simiae infection which have important diagnostic and therapeutic implications.