CC Nov 2015 Mycobacterium Avium Complex (MAC)

echoecho's version from 2015-12-13 19:51


Question Answer
Describe mycobacteria as to whether they are aerobic vs anaerobic? motile vs. nonmotile? thick vs. thin cell walls? hydrophilic vs. hydrophobic cell walls?1) aerobic 2) nonmotile 3) thick cell walls 4) hydrophilic cell walls
What does this organism form that in conjunction with their cell walls reduces the penetration of disinfectants and antibiotics?biofilms
List 5 subspecies?1) M. avium 2) M. silvaticum 3) M. hominissuis 4) M. paratuberculosis 5) M. intracellulare
Mycobacterium is the most common nontuberculosis mycobacterium that infects what part of the body?lungs
Is MAC ubiquitous in the environement? Epidemiologic studies demonstrate widespread exposure in the US especially in what part of the US?1) yes 2) southeast
MAC is found in what part of our environment? Has there been any animal to human transmissions?1) soil and water 2) no
Like all mycobacterium, is MAC easy to culture?no
Mode of transmission has not been well defined, although what is it postulated to be spread by?aerosolizations of droplets small enought to enter the alveoli (hot tubs, showers, irrigation systems, hosipital nebulizers)
Is infection with MAC common?no
List disease states that can make that patient at high risk for disseminated disease1) HIV 2) profound neutropenia (CD4 T-lymphocyte count < 50 cells/uL)
List the lung diseases that increase the risk of MAC infection?1) COPD 2) silicosis 3) prior TB infection 4) cystic fibrosis 5) lung transplants
The use of what drug in the treatment of rheumatic disorders has been associated with the MAC infection?tumor necrosis factor (TNF)-alpha receptor anatagonists
MAC infections may present in a variety of clinical scenarios with non-specific symptoms of what?1) cough 2) fatigue 3) purulent or bloody sputum 4) fever if present is mild
List the 3 identified forms of MAC with the typical patient they are found in?1) upper-lobe fibrocavitary disease (most common) seen in older men with underlying structural lung disease like COPD 2) nontuberculous mycobacterial (NTM) infection may be present as a nodular bonchiectasis typically in elderly, thin women w/o underlying lung disease who may have pectus excavatum, scoliosis and mitral valve prolapse 3) hypersensitivity pneumonitis related to inhaled aerosolized organisms from water sources (hot tub pneumonitis)
Are there any pathognomonic findings on CXR?no; however, fibrocavitary lesions are common
The lesions are often where in the lungs and are ____ (thick vs thin walled) and associated with what abnormalities?1) upper lobes of the lungs 2) thin-walled 3) pleural
In the bronchiectatic variety, CT scan of the chest may show what?clusters of small nodules (the "tree bud" sign)
*** Why is a single pulmonary culture specimen positive for the infection insufficient to confirm disease?because exposure to MAC is so common
*** Diagnosis requires what?1) culture growth from either one bronchoalvelar lavage specmen 2) two sputum samples or material from respiratory tissue demonstrating granulomatous histopathology
Can tuberculin skin testing (TST) using purified protein derivative (PPD) distinguish between tuberculosis and MAC?no
What is the treatment goal in antibiotic therapy of MAC?persistence of negative sputum cultures
Treatment should be maintained for at least ____ year(s) after negative cultures are documented?one
What antibiotics have demonstrated effectiveness against MAC and an ability to penetrate infected tissues?1) azithromycin (Zithromax) 2) Clarithromycin (Biaxin)
What does the antibiotic choice depend on?1) type of pulmonary infection 2) possibility of reinfection 3) severity of the disease
What is the standard of care for treatment of MAC?Triple antibiotic therapy (Macrolide + Ethambutol (Myambutol) + rifampin (Rifadin)
Which of the 3 forms of MAC is easiest to treat? What is the treatment schedule and why?1) nodular bronchiectasis 2) 3x/week schedule 3) to limit side effects and improve patient compliance
Fibrocavitary disease and more severe cases of nodular bronchiectasis should be treated with what?daily triple therapy with consideration of substituting rifabutin (Mycobutin) for rifampin, and with addition of streptomycin or amikacin (Amikin) if needed
*** While marolide-based therapy may reduce the number of exacerbations and the tenacity of sputum in bronchiectatic patients, what is it also associated with?macrolide-resistant MAC
Relapses and reinfection is common and usually represents what?involvement with resistant organisms
Why are patients often underweight?due to underlying chronic lung disease, immunocompromised state or other factors
Why should patient's weight be monitored carefully during treatment?treatment may induce nausea, vomiting, and anorexia and further reduce their weight
Does Isoniazid have a role in treatment of MAC?no
Patients with HIV infection who are diagnosed with disseminated MAC infection and who are not currently receiving antiretroviral therapy (ART) should be treated how? Why?1) treat for MAC x 2 weeks PRIOR to initiating antiretroviral (ART) 2) because this strategy decreases the risk of immune reconstitution inflammatory syndrome (IRIS)
Asymptomatic patients with HIV infection should be offered prophylaxis for MAC once what occurs? CD4 T-lymphocyte count is < 50 cells/uL
Once started, what is the recommendation for prophylactic therapy?be continued until the CD4 count is > 100 cells/uL for > 3 months
The recommended prophylaxis int he order of preference?1) azithromycin 1,200 mg orally every week 2) Clarithromycin 500 mg BID 3) Rifabutin 300 mg daily
*** SUMMARY = Is MAC ubiquitous in the environment? Is there widespread exposure through the US? Is infection common?1) yes 2) yes 3) no
*** SUMMARY = List the disease states that provide an increased risk of MAC?1) HIV 2) profound neutropenia 3) COPD 4) cystic fibrosis 4) underlying lung diisease
*** SUMMARY = Can TST (tuberculin skin testing) using purified protein derivative (PPD) distinguish between tuberculosis and MAC?no