Pneumocystis Carinii Pneumonia

Because of its association with human immunodeficiency virus (HIV) infection, Pneumocystis carinii pneumonia (PCP), an opportunistic infection, has increased in incidence since the 1980s. Before the advent of PCP prophylaxis, this disease was the first clue in about 60% of patients that HIV infection was present.

PCP occurs in up to 90% of HIV infected patients in the United States at some point during their lifetime. It is the leading cause of death in these patients. Disseminated infection doesn't occur.

PCP also is associated with other immunocompromised conditions, including organ transplantation, leukemia, and lymphoma.

Causes

P. carinii, the cause of PCP, usually is classified as a protozoan, although some investigators consider it more closely related to fungi. The organism exists as a saprophyte in the lungs of humans and various animals.

Part of the normal flora in most healthy people, P. carinii becomes an aggressive pathogen in the immunocompromised patient. Impaired cellmediated (T-cell) immunity is thought to be more important than impaired humoral (B-cell) immunity in predisposing the patient to PCP, but the immune defects involved are poorly understood.

The organism invades the lungs bilaterally and multiplies extracellularly. As the infestation grows, alveoli fill with organisms and exudate, impairing gas exchange. The alveoli hypertrophy and thicken progressively, eventually leading to extensive consolidation.

The primary transmission route seems to be air, although the organism is already resident in most people. The incubation period probably lasts for 4 to 8 weeks.

Signs and symptoms

• fever
• cough -- often mild and dry
• shortness of breath -- especially with exertion (activity)
• rapid breathing

Diagnosis

A doctor can sometimes diagnose pneumocystis pneumonia by X-ray or by finding the organism in lung fluids that have been examined in the laboratory. The doctor may need to use a bronchoscope to take a tissue sample from inside the child's lungs. This sample can be sent to a laboratory where special chemical stains can identify the pneumocystis organism.

Even if your child has no other medical problems, call your child's doctor immediately if your child has unusually rapid breathing or difficulty breathing, is coughing, or has a blue or gray color to his or her nails, lips, or skin.

Treatment

PCP may respond to drug therapy with cotrimoxazole or pentamidine isethionate. Because of immune system impairment, many patients who also have HIV experience severe adverse reactions to drug therapy. These reactions include bone marrow suppression, thrush, fever, hepatotoxicity, and anaphylaxis. Nausea, vomiting, and rashes are common. Diphenhydramine may be prescribed to treat the latter effects and leucovorin may reduce bone marrow suppression (and may be used prophylactically in patients with HIV infection).

Pentamidine may be administered I. V. or in aerosol form. I.V. pentamidine is associated with a high incidence of severe toxic effects. The inhaled form usually is well tolerated. However, inhaled pentamidine may not effectively reach the lung apices. Adverse reactions associated with inhalation include metallic taste, pharyngitis, cough, bronchospasm, shortness of breath, rhinitis, and laryngitis.

Supportive measures, such as oxygen therapy, mechanical ventilation, adequate nutrition, and fluid balance, are important adjunctive therapies.

Prevention

Preventive therapy is recommended for AIDS patients, for individuals on chronic high dose corticosteroids, as well as individuals with previous episodes of PCP.

While the most effective preventive drug is trimethoprim-sulfamethoxazole, other options include dapsone, atovaquone, and pentamidine.