Mycobacterial Flashcards
Atypical Mycobacteria - Presentation
Common presentation - chronic pulmonary disease resembling tuberculosis (occurring mainly in adults)
Cervical adenopathy/lymphadenitis in children (M avium-intracellulare complex,M scrofulaceum)
Mycobacterium marinumis the causative agent of swimming pool granuloma
Tenosynovitis , bursae, bone and joint infections by both rapidly and slow-growing MAC andM marinumseen in tenosynovitis of the hand
Osteomyelitis of the sternum caused byM abscessusfound in clustered and sporadic outbreaks
M fortuitumandM chelonaerapidly growing strains, occasionally seen in wound, soft tissue, pulmonary, and middle ear infections
Atypical Mycobacteria - Clinical
Most common presentation in immunocompetent pediatric host - suppurative cervical or submandibular lymphadenopathy with/without systemic symptoms
M avium-intracellulare
M scrofulaceum
Fistula may occur with coalescence of involved cervical or mandibular nodes
In children infected with HIV
Most common - recurrent and persistent fever and chronic anemia
Less frequent - chronic diarrhea and recurrent abdominal pain
Catheter-related infections most common nosocomial nontuberculous mycobacterial infections (fast-growing atypical mycobacteria, e.g.M fortuitum,cause most catheter-related infections)
Atypical Mycobacteria - Workup
Organisms from blood, biopsy material, bone marrow, and stools grow on routine bacterial media,
Better growth on selective mycobacterial media
Nucleic acid hybridization probes using target sequences or ribosomal RNA for rapid identification of clinical isolates
Species can be identified using high-performance liquid chromatography or biochemical tests
Polymerase chain reaction (PCR)-restriction analysis of clinical isolates have been used for the identification ofM kansasii
DisseminatedM aviumcomplex (MAC) disease is most commonly diagnosed using culture of blood and bone marrow or other normally sterile tissues or body fluids
Immunocompetent patients, CXR mimics reactivation tuberculosis
Second presentation includes the presence of patchy nodular infiltrates, without cavities in a nodular distribution
CT of lung detects bronchiectasis
CT of abdomen shows multiple enlarged retroperitoneal and mesenteric lymph nodes
Fine-needle percutaneous aspiration to confirm the diagnosis
Surgical Treatment- Atypical Mycobacteria
Surgical excision of infected nodes is recommended for immunocompetent children with suppurative adenitis secondary toM aviumcomplex (MAC) andM scrofulaceum
I&D of fluctuant abcesses often leads to a draining sinus lasting months or years
Medications- Atypical Mycobacteria
Treatment disseminated MAC in HIV includes at least 2 antimicrobials, one being clarithromycin or azithromycin
Ethambutol preferred as 2nd drug
3rd or 4th antibiotic possible: clofazimine, rifabutin, ciprofloxacin, or amikacin
Rx for disseminated MAC disease may need to be continued for life unless sustained immune recovery with potent antiretroviral therapy
Tuberculosis Overview
Mycobacterium tuberculosis (slow-growing, obligate aerobe, facultative, intracellular parasite – ‘red boxcars’)
Incidence of TB was declining since the early 20th century, primarily infection-control practices (quarantine)
Mid-1980s resurgence in ethnic minorities and HIV infected individuals (20-40 fold increased risk of TB)
MDR-TB is defined as resistance to the 2 most effective first-line drugs: isoniazid & rifampin
Extensively drug-resistant TB (XDR-TB), is resistant to isoniazid, rifampin, and second-line drugs used to treat MDR-TB (mortality rates similar to preantibiotic era)
TB is often not appropriately considered or patient isolated in OP or ED settings
Infectivity is high, e.g. a case of active TB in a young child indicates disease in 1 or more adults with close contact
Tuberculosis Pathophysiology
M tuberculosisusually contracted infected aerosol exposure through the lungs or mucous membranes
Immunocompetent individuals
Only 5 % show clinical disease
Rest (95%) latent/dormant infection
Decreased immune response allows M tuberculosis reactivation
Disease results from direct bacterial effects & inappropriate host immune responses to tubercular antigens
Molecular typing in US shows > 1/3 of new patient occurrences of TB result from person-to-person transmission; remainder 2/3s from reactivation of latent infection
M tuberculosissurvives and proliferates within mononuclear phagocytes that ingest the bacterium, allows M tuberculosisto invade local lymph nodes and spread to extrapulmonary sites via hematogenous routes (bone marrow, liver, spleen, kidneys, bones & brain)
Presentation of Tuberculosis
85% of patients with TB present with pulmonary complaints
Most common sites of extrapulmonary disease are mediastinal, retroperitoneal, and cervical (scrofula) lymph nodes; vertebral bodies, adrenals, meninges, and the GI tract
Infected end organs typically have high, regional oxygen tension (as in the kidneys, bones, meninges, eyes, and choroids, and in the apices of the lungs)
Principal cause of tissue destruction fromM tuberculosis- organism’s ability to incite intense host immune reactions to antigenic cell wall proteins
TB lesion is epithelioid granuloma with central caseation necrosis (primary lesion commonly within alveolar macrophages in subpleural regions of the lung; bacilli proliferate locally and spread through the lymphatics to a hilar node, forming the Ghon complex
Early Tubercles
spherical, 0.5- to 3-mm nodules; 3 or 4 cellular zones
central caseation necrosis
inner cellular zone of epithelioid macrophages and Langhans giant cells admixed with lymphocytes
outer cellular zone of lymphocytes, plasma cells, and immature macrophages
rim of fibrosis (in healing lesions)
Tuberculosis Epidemiology
50.4% of TB cases reported from 4 states: California, Florida, New York, and Texas
2011, more than 60% of cases of TB reportedly occurred among foreign-born persons, 54% cases in 2011 identified in persons from 5 countries: Mexico (21.3%), the Philippines (11.5%), Vietnam (8.2%), India (7.6%), and China (5.6%)
Estimated 10-15 million people in the United States have latent TB infection
Globally, > 1/3 of the population is infected with tubercle bacillus
Factors that increase likelihood PT has TB
HIV infection
History of a positive purified protein derivative (PPD) test result
History of prior TB treatment
TB exposure
Travel to or emigration from a TB endemic area
Homelessness, shelter-dwelling, incarceration
Features of active TB
Cough Weight loss/anorexia Fever Night sweats Hemoptysis Chest pain Extrapulmonary involvement in 20% of all TB cases 60% of extrapulmonary cases have no pulmonary symptoms; negative CXR or sputum
Scrofula
Nodular lesion with caseous exudate on chest. Mycobacterium tuberculosis
Presentation of Pulmonary TB
Productive cough, fever, and weight loss; occasionally hemoptysis or chest pain, anorexia, fatigue, and night sweats
Tuberculosis Meningitis Presentation
Intermittent or persistent headache for 2-3 weeks
Subtle mental status changes may progress to coma over a period of days to weeks
Fever minimal or absent
Thick grey exudate encasing CNs and blood vessels
