Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (484 page)

   
Mycobacterium kansasii
:
M. kansasii
infection presents as pulmonary disease that may be difficult to distinguish from TB. Most patients present with chest pain and fever. Hemoptysis, fever, and night sweats are also common. Cavitation is commonly seen on chest x-ray.
Mycobacterium kansasii
, in contrast to other NTM, is not found in soil or natural water sources but is associated with tap water in cities where the organism is endemic.

   
Mycobacterium marinum
:
M. marinum
is well described as a cause of chronic cutaneous infection after exposure to water sources, the so-called fish tank granuloma.

   Organisms enter through traumatic or preexisting breaks in the skin surface. Several weeks after exposure, a nodular or ulcerating lesion develops at the site of infection, with subsequent spread along lymphatic channels. Infections usually occur on the extremities, most often the hands. The infection may be locally invasive but usually only in immunocompromised patients.

   Diagnosis may be established by AFB smear and culture. Note that
M. marinum
(and other NTM that are mainly associated with cutaneous infection) grows optimally in cultures incubated at 30°C, so special AFB cultures should be requested. Histopathologic examination shows granuloma formation.

   Laboratory Findings

AFB smear and culture of lower respiratory samples
. ATS/Infectious Disease Society of America (IDSA) criteria to confirm NTM pulmonary infection:

   Positive culture from two or more expectorated sputum samples

   Positive culture from one or more BAL or bronchial wash samples

   Lung biopsy consistent with mycobacterial infection (granulomatous inflammation or AFB), confirmed by positive culture of tissue or respiratory specimen

   Positive culture from a normally sterile, nonpulmonary site of infection

AFB smear and culture of infected material from nonpulmonary sites
: When NMT infection is suspected, AFB smear and culture of specimens taken from infected, nonpulmonary sites, especially normally sterile sites, are recommended. Ensure that an adequate quantity of sample is submitted for AFB culture; repeat testing of sequential specimens is likely to improve isolation.

Blood culture
: The diagnosis of disseminated NTM infection is usually efficiently established in immunocompromised patients by submission of AFB blood cultures. AFB culture of bone marrow may also be diagnostic, especially in immunocompromised patients with hematologic abnormalities.

Susceptibility testing
:

   MAC: clarithromycin only

   
Mycobacterium kansasii
: rifampin only

   RGM: amikacin, imipenem (
M. fortuitum
), doxycycline, fluoroquinolones, sulfonamide or TMP/SMX, cefoxitin, clarithromycin, linezolid, tobramycin (
M. chelonae
)