Page 96 - AIDSBK23C

Page 96

Acid fast smear microscopy is less frequently positive in patients infected with HIV and
MTB. In people infected with HIV, a third sputum smear does not improve the diagnostic yield
for MTB. Broth-based culture of three sputum specimens diagnoses most pulmonary MTB cases.
Broth-based culture of sputum identified substantially more cases than microscopy or solid
media culture. A single sputum cultured on broth yields as many positive results as three sputum
samples cultured on solid media. Lymph node aspiration provides the highest incremental yield
of any non-pulmonary specimen test for MTB.[437]
Microscopic detection of MTB is aided by fluorescence microscopy. The use of an
auramine fluorescent stain for mycobacteria requires a microscope with fluorescence attachment.
Newer epifluorescent microscopes are easier to set up and use. Most new fluorescence units
employ filters that pass fluorescent light that only provides visualization for the auramine
component of the stain, in contrast to the wide band filters of older units. The fluorescent stain is
more sensitive than acid fast stains by light microscopy. False positive results can be avoided by
careful interpretation.[431]
In persons converting to a positive skin test, a 12-month course of isoniazid is
recommended, with use of rifampin for patients unable to tolerate isoniazid. HIV-infected
persons who are close contacts of persons infected with tuberculosis may begin to receive
prophylactic therapy, and a decision to continue therapy can be made after skin testing and
follow up. For patients with newly diagnosed tuberculosis, a four-drug regimen consisting of
isoniazid, rifampin, pyrazinamide, and either streptomycin or ethambutol is recommended, with
therapy lasting at least 9 months (at least 6 months after sputum cultures are negative). For
patients exposed to multiple-drug resistant MTB, therapy for 12 months with high dose
ethambutol with pyrazinamide and ciprofloxacin is recommended. [208,429,432] The use of
bacille Calmette-Guérin (BCG) vaccine in patients with HIV infection may not recommended
because of the risk for disseminated disease.[438]
The organ distribution of MTB in AIDS is widespread. Extrapulmonary MTB is found in
70% of patients with a CD4 lymphocyte count less than 100/µL and in 28% of those with a CD4
lymphocyte count greater than 300/µL At autopsy, the respiratory tract is involved most
frequently, followed by spleen, lymph node, liver and genitourinary tract. Bone marrow,
gastrointestinal tract, and adrenal are less common sites of involvement. Mycobacterium
tuberculosis is uncommonly identified in central nervous system, heart, and skin (Table
5).[417,429]
The clinical presentation of MTB in AIDS can resemble that of non-AIDS patients, and
MTB can often be the first AIDS-defining illness, particularly in regions where the incidence of
MTB is high in the general population. Tuberculosis should be suspected in patients with fever,
cough, night sweats, and weight loss, regardless of chest roentgenogram findings. In patients
with residual immune function, with a CD4 count >200/µL, MTB resembles reactivation
tuberculosis, with cavitation and upper lobe infiltrates on chest roentgenography, and tuberculin
skin tests are often positive. With severe immunosuppression and CD4 counts below 200/µL,
hilar adenopathy, pleural effusions, lack of cavitation or consolidation but presence of a miliary
pattern more typical of primary MTB infection appear.[428,439]
Tuberculin skin tests may be falsely negative. Pulmonary symptoms can also include
hemoptysis, chest pain, and dyspnea. Differentiation from P jiroveci (carinii) or fungal infection
can be difficult, but both sputum and blood cultures are useful for diagnosis. Extrapulmonary
MTB often produces fever, weight loss, and lymphadenopathy, and the yield from lymph node
aspiration biopsy is high.[428,429] Clinical features that help to distinguish disseminated MTB