Page 95 - AIDSBK23C

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levels of IL-10 can be increased, leading to upregulation of the apoptosis inhibitor BCL3. When
HIV infects macrophages, autophagy is inhibited, along with intracellular killing of
mycobacteria.[431]
Unlike MAC, though, striated macrophages are not a common feature with multiple drug
resistant MTB. Patients with multiple drug resistant MTB have extrapulmonary dissemination in
a third of cases, and their survival from the time of diagnosis is two months or less. Despite
therapy with multiple agents, most patients will continue to have intermittently or persistently
positive sputum cultures, indicating that such resistant MTB pose a considerable risk to other
patients and to health care workers.[147]
Yearly skin test screening with 5 TU of purified protein derivative (PPD) is
recommended in previously PPD-negative persons. Only 10% of persons with a CD4
lymphocyte count >500/µL are likely to exhibit anergy, though a positive test in HIV-infected
persons should be defined as any area of induration >0.5 cm (or >0.2 cm for injection drug
users). Anergy may be detected by companion testing with Candida, mumps, or tetanus toxoid
skin tests. Patients suspected of having tuberculosis should be evaluated further with a chest
roentgenogram and have at least three sputum specimens collected to detect acid-fast
bacilli.[208]
Rapid whole-blood tests have been developed that employ an ELISA or enzyme-linked
immunosorbent spot assay to measure the interferon-gamma (IFN-gamma) release of sensitized
T lymphocytes in response to previously encountered mycobacterial antigens. Such tests have
shown cross-reactivity to Mycobacterium marinum and to Mycobacterium kansasii but not to
Mycobacterium avium-complex or to bacille Calmette-Guérin (BCG). The sensitivity for active
tuberculosis in HIV-infected persons has been reported as 91%.[436] IFN-gamma release assays
do not help to distinguish latent from active TB.[431]
Mycobacterial infections can also be detected with tissues or cytologic material obtained
via bronchoalveolar lavage, transbronchial biopsy, and fine needle aspiration. Acid-fast bacilli
(AFB) staining along with culture remains the standard procedure for detection of MTB. The
AFB stains commonly employed include the Ziehl-Neelsen and Kinyoun carbolfuchsin methods.
False positive results can occur when the carbolfuchsin stain precipitates on short segments of
cellular debris. Interpret as acid-fast bacilli only those structures that are uniformly and evenly
stained throughout their length. Some morphologic variability exists among different species of
mycobacteria. False negative results can be avoided by searching the slide carefully for many
minutes. Using a positive control that does not have numerous organisms will help to avoid
under staining and give an indication of how difficult the search can be.
Liquid culture is more sensitive and rapid than MTB culture on solid media. Culture
requires a greater incubation time compared with that for non–HIV-infected patients, consistent
with lower bacillary load of sputum specimens. Urine detection of the mycobacterial cell wall
component lipoarabinomannan may improve detection in smear-negative HIV-infected patients
with advanced immunosuppression.[431]
The polymerase chain reaction (PCR) to mycobacterial DNA can be performed in
selected cases. If disseminated tuberculosis is suspected, then cytologic or histologic material
obtained from extrapulmonary sites should also be cultured for MTB.[208,429] Rapid, but
expensive, tests for detection of MTB are available that are based upon the detection of DNA or
ribosomal RNA from MTB organisms. These rapid tests yield results in less than a day, but do
not replace acid fast staining, which can provide an index of contagiousness, or mycobacterial
culture, which indicates drug susceptibility.[428]