Laboratory diagnosis of nontuberculous mycobacteria.

Even in the twenty-first century, mycobacterialdiseases continue to cause serious public healthproblems. Although the number of cases of tuber-culosis are decreasing in the United States, nontuber-culous mycobacteria (NTM) are being recovered withincreasing frequency from both immunocompro-mised (ie, HIV infected, cystic fibrosis patients) andimmunocompetent patients. The clinical significanceof these isolates has to be determined in each casebecause NTM are prevalent in the environment [1].NTM were not traditionally considered a threat topublic health, as person-to-person transmissionoccurs rarely if at all, yet these organisms canproduce serious morbidity. In addition, cases ofmycobacterial disease are becoming more difficultto diagnose or treat, especially when fastidious NTMor drug-resistant strains are involved [2,3].Because of the increasing number of immunocom-promised patients, immigrants, refugees, patients incongregate settings, and patients with drug-resistantdisease, a wide array of clinical and public healthspecialists are required. The modern mycobacteriol-ogy laboratory plays a critical role in the laboratorydiagnosis of tuberculosis and also diseases caused byNTM. These services must be accelerated andexpanded not only in response to the changes inpatient populations, but also to fulfill the need forshorter turnaround times that result in savings oflimited health-care resources.The most urgent questions that need to be ad-dressed rapidly by the mycobacteriology laboratoryinclude: (1) are tubercle bacilli orNTM involved?; (2)if NTM are involved, based on the existing clinicalinformation (clinical, radiographic, and histologicalappearance, site of the disease, and source of speci-men) and laboratory findings, does the isolated and/oridentifiedNTMhaveanyclinicalsignificance?;(3)ifaclinically significant NTM is involved, are effortsmade to ensure a rapid identification?; and (4) ifMycobacterium avium complex, M kansasii, M fortu-itum, M abscessus, or M chelonae are identified asclinically significant isolates, are susceptibility testassays performed according to standard procedures?Twenty-five years ago, the Mycobacterium genuscomprised only some 30 species. At present, itencompases close to 100 [4]. The most recentlydescribed NTM species that are involved in pulmo-nary disease are listed in Table 1 [5–18]. Previously,the identification of NTM seemed to be feasible usinga panel of cultural characteristics and biochemicaltests [3]. The recent plethora of newly describedspecies poses, however, an additional challenge for