The risk of<unk>  increases when CD4-positive T-cell levels are less than 400 cells/μL. In these immunosuppressed individuals, the manifestations of the infection are highly variable. The disease attacks the interstitial, fibrous tissue of the lungs, with marked thickening of the alveolar septa and alveoli, leading to significant hypoxia, which can be fatal if not treated aggressively. In this situation, lactate dehydrogenase levels increase and gas exchange is compromised. Oxygen is less able to diffuse into the blood, leading to hypoxia, which along with high arterial carbon dioxide () levels, stimulates hyperventilatory effort, thereby causing dyspnea (breathlessness).
Pneumocystis pneumonia
Pneumonia alba
Tuberculosis
Allergic bronchopulmonary aspergillosis
Histoplasmosis
Fungal pneumonia
Aspergillosis
Primary pulmonary coccidioidomycosis