Mycobacterium kansasii: colonization and disease.

Mycobacterium kansasii has a wide range of virulence from fatal disease to infection and colonization. The laboratory report of growth of M. kansasii is often a problem for the clinician and an encumberance for the patient. To determine the difference between patients who had disease from M. kansasii and those from whom it was isolated without causing disease, we compared the records of 70 patients from whom this mycobacterium was isolated. The group with disease was defined as those patients with more than one culture with luxuriant growth and new, compatible symptoms, signs or radiographic changes. Age, sex, occupation, place of birth and residence, past medical history, skin testing, radiographic changes, in vitro antibiotic sensitivities, and the time and source of the isolation were tabulated. The group without compatible disease had only a single isolate and almost never had any new symptom or sign. Patients with disease from M. kansasii were more often male (P less than 0.02) and had more chronic obstructive lung disease (P less than 0.001). Patients without disease more frequently had isolations from laryngeal swabs (P less than 0.001). The cultures of these swabs had less stringent laboratory decontamination. M. kansasii may be a more frequent colonizer of the upper airway than previously thought. Clinicians should use the same rigorous definition of disease caused by M. kansasii as clinical investigators, namely repeated isolations with luxuriant growth in an appropriate host. The laboratory, instead of the clinician, should investigate positive cultures in patients without disease.