Most species in this group are less virulent than TB and usually affect immunocompromised hosts.
Risk factors for pulmonary disease include bronchiectasis, scoliosis, pectus excavatum, mitral valve prolapse, and cystic fibrosis.
HIV and use of anti-TNF drugs are associated with disseminated disease.
Nosocomial infections are associated with inoculation into the skin during surgical procedures such as cosmetic facial surgery, ophthalmic surgery (including LASIK), augmentation mammoplasty, median sternotomy, and liposuction.
These mycobacteria do not cause latent infection, and there is no person-to-person transmission risk.
Routes of infection include cutaneous, respiratory, GI, and parenteral.
Isolation from clinical specimens may represent colonization, true infection, or contamination.
M. kansasii and M. szulgai are almost always true pathogens when isolated from respiratory specimens.
M. simiae and M. fortuitum are usually not respiratory pathogens (except in patients with chronic vomiting and aspiration) even if the nontuberculous mycobacterial diagnostic criteria are met.
M. gordonae and M. terrae complex are almost always contaminants of respiratory specimens.
Divided into slow growers and rapid growers depending on speed of growth on culture media
Rapid growers group include M. abscessus, M. fortuitum, and M. chelonae and usually grow within 7 days.
Slow growers group include M. kansasii, M. marinum, M. ulcerans, M. szulgai, and other rare mycobacteria. This group requires at least 2 to 3 weeks to grow.
Some species may cause false-positive PPD and interferon release assays, such as M. kansasii, M. marinum, and M. szulgai.
Table 65-1 Atypical Mycobacteria: Presentation and Treatment
Organism
Presentation
Treatment
Comment
Slow growing M. kansasii
Pulmonary disseminated
INH + rifampin + ethambutol
Clarithromycin, moxifloxacin, sulfamethoxazole, streptomycin also active and may be used for rifampin-resistant isolates
M. marinum
Skin lesions
Ethambutol + rifampin or clarithromycin
Minocycline-doxycycline and trimethoprim-sulfamethoxazole are also active, may need debridement
M. ulcerans
Skin disseminated
Mainly surgical debridement clarithromycin + rifampin to prevent relapse
Causes necrotic skin and soft tissue lesions (“Buruli” ulcer)
M. xenopi
Pulmonary disseminated
Clarithromycin + rifampin + ethambutol
Grows at higher temperatures (45°C); quinolones may be added for better response.
M. szulgai
Pulmonary, tenosynovitis, osteomyelitis
INH + ethambutol + rifampin
Always a potential pathogen favorable treatment outcomes
Rapid growing M. abscessus
Pulmonary Skin
Clarithromycin + amikacin + cefoxitin
Pulmonary disease difficult to treat Imipenem may be a substitute for cefoxitin.
M. chelonae
Skin disseminated, catheter-related
Clarithromycin ± imipenem or tobramycin
Resistant to cefoxitin, can lead to contact lens-associated keratitis
M. fortuitum
Skin, catheter-related, rarely pulmonary
Clarithromycin + doxycycline or trimethoprim-sulfamethoxazole or quinolone
Start with IV agent (amikacin + imipenem or cefoxitin) for serious infections
Contains erm gene (inducible macrolide resistance); associated with gastroesophageal disorders such as achalasia; can lead to nail salon furunculosis
Antibiotic susceptibility testing should be done for rapidly growing NTM species to guide therapy.
Susceptibility testing is not needed for slowly growing NTM except for M. kansasii susceptibility to rifampin. In other species, there is no correlation between susceptibility tests and in vivo response to antimicrobials.
Considered the second most common cause of NTM disease in the United States and the most pathogenic
Tap water is the major environmental reservoir.
Divided into five to seven subspecies; serotype 1 is the major isolate responsible for human infections.
Primarily affects middle-aged white men
Risk factors include pneumoconiosis, COPD, previous mycobacterial disease, malignancy, and alcoholism.
The combination of HIV infection and silicosis increases the susceptibility to M. kansasii.
Pulmonary infections resemble the clinical course of MTB, with similar symptoms.
Symptoms include cough and sputum production, hemoptysis, fever, night sweats, and weight loss.
Chest x-ray changes are usually located in the lung apices and include cavitation (in 50% of cases), pleural scarring, and infiltrates.
The same diagnostic criteria for MAC apply to infections with other NTM, including M. kansasii.
Growth of M. kansasii in a single sputum culture should potentially represent true infection, especially in HIV-infected patients.
Dissemination occurs in about 25% of HIV-infected patients, usually with a CD4 count of <50 cells/µL.
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