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diagnosis. Urine serologic titers for L pneumophila antigen are 90% sensitive and 99% specific
for diagnosis.[633]
Rhodococcus equi has been recognized as a pathogen in persons with HIV infection, and
it can be missed because it sometimes stains weakly acid fast or resembles contaminant
diphtheroids on gram stain. It is a facultative intracellular bacterium that proliferates within
macrophages.[634] HIV-infected patients with R equi have a mean CD4 lymphocyte count of
50/µL. The most common symptoms are fever and cough. Pathologic findings include
pneumonia in 82%, cavitary lesions in 69%, lung abscess in 9%, pleural effusion in 6.5% and
empyema in 2.3%. Extrapulmonary lesions may be found in 20% of cases, including brain
abscess, soft tissue infection, septicemia, lymphadenitis, and pericarditis. Radiologic findings
most often include a localized pneumonia with consolidation and cavitation. The persistence of
R equi in macrophages can also lead to the appearance of pulmonary malakoplakia.
Malakoplakia is a form of granulomatous inflammation marked by the appearance of Michaelis-
Gutman bodies, which are target-like calcospherites, within macrophage cytoplasm.
[499,505,635]
Septic emboli involving the lungs are typically caused by bacterial organisms. The
radiographic appearance includes a peripheral or subpleural distribution of 1 to 2 cm nodules.
Cavitation within nodules or wedge-shaped opacifications from infarction can occur.[606]

VIRAL PNEUMONITIS.-- Aside from cytomegalovirus, other viral infections of lung
are less frequently diagnosed, though the true incidence remains unknown. Viruses may be
recovered from bronchoalveolar lavage fluid. Viral pneumonitis may be difficult to distinguish
from non-specific interstitial pneumonitis or lymphoid interstitial pneumonitis without specific
viral cultures or serologies. Bacterial infections often complicate viral pneumonitis and may be
indistinguishable clinically, though a viral pathogen may be the only infectious agent present in
some cases. Viral pneumonias most frequently are due to herpes simplex, rhinovirus, influenza,
parainfluenza, and adenovirus in adults, with respiratory syncytial virus more frequent in
children. Mycoplasma species, though not viruses, can produce a similar clinical picture with
infection, and can also be recovered with bronchoalveolar lavage.[636] Vaccination against
influenza is recommended for all HIV-infected persons.[208,637]
Human herpesvirus 6 (HHV-6) infects at least 90% of all persons by two years of age and
can reactivate in immunocompromised hosts to produce a severe pneumonitis. Such reactivation
of latent infection in persons with AIDS may be the cause for a fatal pneumonitis. HHV-6 can
be found in other tissues as well, and lymphoid tissues are the reservoir for HHV-6 infection.
HHV-6 can be demonstrated in tissues by immunohistochemical staining.[638]

KAPOSI SARCOMA (KS).-- The clinical diagnosis of pulmonary KS can be difficult
because KS is difficult to distinguish from opportunistic infections. The diagnosis is made more
likely when a previous skin biopsy has demonstrated KS. Most patients with pulmonary KS will
present with fever, non-productive cough, and dyspnea. Hemoptysis and chest pain are
additional common findings. Hoarseness and stridor may suggest upper airway involvement of
larynx and trachea.[547]
Radiographic findings are not specific and may include bilateral perihilar and lower lobe
reticulonodular, interstitial, or alveolar infiltrates in over half of cases. The presence on chest
radiograph of abnormal hilar densities with perivascular or peribronchial extension into adjacent
pulmonary parenchyma is suggestive of KS. Also, a bronchocentric pattern of bronchial wall