Causes and Incidence
Pneumocystis carinii, the cause of this type of pneumonia, is a fungus. The disease (PCP, or pneumocystosis) was relatively rare, seen in only a handful of severely immunosuppressed patients, until the advent of AIDS. PCP is now seen in about 80% of individuals with AIDS and is the initial AIDS-defining condition in more than 60% of HIV-positive individuals.
The fungus lies dormant in the person’s lung until the body’s defenses are compromised. At that time a usually benign resident becomes an aggressive pathogen. The organisms proliferate in the alveolar spaces, facilitated by diminished cell-mediated and humoral host defenses. The organisms attach to alveolar epithelial cells, impairing replication and inducing degeneration and increased membrane permeability. This causes formation of exudate in the alveolar space, reduces surfactant levels, and results in intrapulmonary shunting of blood, decreased lung compliance, and hypoxemia.
Fever, dyspnea, and a dry, nonproductive cough that evolves over several days or weeks are the first symptoms. Increasing shortness of breath usually prompts the individual to seek treatment. The onset tends to be more acute in individuals who do not have AIDS.
Potential Complications Pulmonary insufficiency, pulmonary failure, and death can occur. The overall mortality rate with treatment is about 20%.
The definitive diagnosis is established through a histopathologic examination, preferably of induced sputum. A chest x-ray examination may show fluffy infiltrates. A gallium scan may show increased lung uptake even if the x-ray is negative.
Antiinfective drugs to combat the pathogen (trimethoprim/ sulfamethoxazole [TMP/SMX] is the drug combination of choice); adjunctive corticosteroid therapy; prophylaxis with TMP/SMX and aerosol pentamidine for AIDS patients who already have had one bout of PCP and in those with a CD4 cell count below 200/mm3.
Oxygen therapy; adequate hydration; adequate ventilation or ventilatory support; adequate nutrition; education of HIV-positive individuals about early signs and symptoms of PCP.