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show either focal or diffuse involvement, with geographic areas of firm orange to yellow-tan
necrosis, hemorrhage, and edema. Aspergillus is readily demonstrated in Gomori methenamine
silver (GMS) and periodic acid-Schiff (PAS) stains by the appearance of 3 to 5 micron diameter
branching Y-shaped septate hyphae of nearly uniform caliber which commonly invade bronchial
walls and blood vessels. Vascular invasion can produce thrombosis and infarction. A poorly
formed granulomatous response at the periphery of the lesions is uncommon.
Aspergillus fungal hyphae can be readily distinguished from Candida by the absence of
budding cells and pseudohyphae in the latter. Aspergillus can be distinguished from
Zygomycetes such as Mucor by the smaller diameter of hyphae and presence of septation in the
former. Hyphae of Mucor are non-septate, short, broad, and have irregular shapes, while
pseudohyphae of Candida are smaller than the branching, finger-like hyphae of Aspergillus. The
various species of Aspergillus can be distinguished by culture, but they all have similar
morphologic appearances in tissue sections as well as similar clinical courses. Amphotericin B
and/or itraconazole are variably effective treatments.[620,623]

NOCARDIOSIS.-- Nocardia, a genus of aerobic actinomycetes, can produce both
localized and disseminated disease, usually late in the course of AIDS. The lung is the most
common site for infection and N asteroides is the most frequent species isolated. Additional The
clinical presentations include subacute sinusitis, chronic localized abdominal abscess, and acute
disseminated nocardiosis. There are no specific clinical findings, though fever, productive
cough, and weight loss are the most frequent findings. On chest radiograph, an alveolar pattern
of pulmonary infiltrates is the most common feature, with reticulonodular patterns seen in fewer
patients. The nodules may be spiculated and cavitated on chest CT, with an associated pleural
reaction. Gross pathologic features may include pneumonic consolidation, abscess formation,
cavitation, and pleural effusions. Microscopically, Nocardia produces an acute inflammatory
response in which the gram-positive filamentous organisms can be identified. The disease may
remain localized or become disseminated to involve such sites as subcutaneous tissues, central
nervous system, and kidney, with resultant high mortality rate. Early diagnosis from culture and
treatment with sulfonamides or minocycline leads to better response and outcome.[606,625,626]

BLASTOMYCOSIS.-- Blastomyces dermatitidis is an uncommon opportunistic
infectious agent, even in endemic areas of the Midwestern and south-central United States and
southern Canada. Infection occurs from inhalation of infective conidia derived from the mycelial
form of the organism that grows in soils with high organic content in humid climates.
Blastomycosis is most often seen when the CD4 lymphocyte count is less than 200/µL. Infection
usually involves the lung. Blastomycosis with HIV infection can manifest as localized
pulmonary disease, but disseminated infection occurs just as frequently and most often involves
the central nervous system, though a wide variety of tissue sites can be affected. Cutaneous
involvement with deep ulcers is less frequent in association with HIV infection than in non-
immunocompromised hosts.[454]
Patients have usually developed a prior AIDS-defining illness, and blastomycosis occurs
as a late or terminal event. Typical presenting symptoms include fever, cough, pleuritic chest
pain, dyspnea, and weight loss. Radiographs are often abnormal with lobar infiltrates, nodules,
miliary pattern, or diffuse interstitial changes. Diagnosis can be made by finding thick-walled,
double-contoured 8 to 20 micron sized yeasts with single broad-based buds in cytologic
specimens or tissue biopsies and by confirmatory culture. Serologic tests are not useful.