Pneumocystis carinii pneumonia


Pneumocystis carinii pneumonia

Description, Causes and Risk Factors:

Abbreviation: PCP.

Pneumocystis carinii pneumonia is an opportunistic infection that occurs in immunosuppressed populations, primarily patients with advanced human immunodeficiency virus [HIV] infection. The classic presentation of nonproductive cough, shortness of breath, fever, bilateral interstitial infiltrates and hypoxemia does not always appear.

Classically, in pneumocystis carinii pneumonia the causative organism was re-classified as pneumocystis jirovecii. Strictly speaking, pneumocystis carinii refers to a species found in rats, while pneumocystis jirovecii refers to the human isolate. However, physicians have been slow to adopt the updated terminology, and there continues to be widespread use of the term PCP.

P jiroveci is now one of several organisms known to cause life-threatening opportunistic infections in patients with advanced HIV infection worldwide. Well over 100,000 cases of PCP were reported in the first decade of the HIV epidemic in the United States in people with no other cause for immunosuppression.

In developing regions of the world, the prevalence of PCP was once thought to be much lower, but studies have shown that the lower reported incidence is likely a failure to accurately diagnose PCP. An accurate diagnosis requires access to modern medical care, which is not available worldwide.

In patients with HIV infection, PCP once carried a mortality rate of 20-40%, depending on disease severity at presentation. Currently, mortality rates of 10-20% are reported. PCP is still a major cause of death in patients with AIDS in the United States.

In persons without HIV infection, PCP carries a worse prognosis; this has not changed significantly in the past 20 years. Mortality rates of 30-50% have been documented in several large studies.

The prognosis of PCP is worse in patients who present with concurrent pulmonary disease, in patients who develop pneumothorax, and in patients who require mechanical ventilation. The higher mortality rate is likely a result of delayed diagnoses and delayed initiation of appropriate treatment.

Symptoms:

Symptoms may include:

    Cough -- often mild and dry.

  • Fever.

  • Rapid breathing.

  • Shortness of breath with exertion (activity).

Diagnosis:

Tests:

    CD4 cell count: Check records for a recent CD4 count (CD4 is <200 cells/µL in >90% of PCP cases). Note that a CD4 count obtained in the setting of acute illness (e.g., when the patient presents with pneumonia) may be substantially lower than the usual baseline, and may be difficult to interpret.

  • Pulse oximetry at rest and after exercise: Oxygen desaturation with exercise suggests an abnormal alveolar-arterial O2 gradient (A-a gradient).

  • Arterial blood gas (ABG): Hypoxemia is common, as is elevation in A-a gradient. Generally, PO2 levels and A-a gradient are associated with disease severity. Poorer outcomes are seen with PO2<70 mm Hg and A-a gradient >35 mmHg.

  • Lactate dehydrogenase (LDH): Elevated serum LDH (>300-500 IU/L) is common.

  • Chest X ray: Typically shows bilateral interstitial infiltrates, but atypical patterns with cavitation, lobar infiltrates, nodules, or pneumothorax may occur, and chest X-ray findings may be normal in some cases. Upper lobe predominance is common if the patient is receiving aerosolized pentamidine for PCP prophylaxis.

  • Thin-section chest computed tomography (CT) scan: May show ground glass opacities; in a patient with clinical signs or symptoms of PCP, these are suggestive but not diagnostic of PCP.

  • Sputum induction: The patient inhales saline mist to mobilize sputum from the lungs. The respiratory therapist collects expectorated sputum, which is stained with Giemsa and examined for P. jiroveci organisms. This technique is useful because of its noninvasive approach, but it requires an experienced technician, and therefore may not be available at all centers. Sensitivity varies widely (10-95%), depending on the expertise level of the staff at a particular center. (If there is any chance that the patient has TB, sputum induction should be performed in a confined space in a negative pressure area or near an exhaust fan vented safely outside, and samples should be sent for acid-fast bacilli [AFB] smear and culture.)

  • Bronchoscopy with bronchoalveolar lavage (BAL): If induced sputum tests negative for PCP organisms, definitive diagnosis is made through detection of organisms in BAL fluid obtained during bronchoscopy. Sensitivity is >95% at centers with an experienced staff. BAL fluid can be evaluated for bacteria, mycobacteria, and fungi, as well as for P. jiroveci.

  • Transbronchial biopsy may be performed if lung disease is progressive despite treatment, to look for diagnoses other than PCP. Open lung biopsy rarely is performed.

Treatment:

Most patients with an acute infection are treated with trimethoprim and sulfamethoxazole, combined with corticosteroids in patients with moderate to severe infections. The same agent may be used as prophylaxis. A number of alternative agents may also be employed, both for acute treatment and for prophylaxis, although these are beyond the scope of this article.

Overall, with prompt treatment, survival is good (50 - 95%), although relapses are common. Even with treatment, about one in five people will die of pneumocystis carinii pneumonia.

Available therapies have many adverse effects, and treatment is more often limited by toxicity than by lack of response. Patients with AIDS require three weeks of treatment for PCP, compared with two weeks in other populations. Hospitalized patients should receive intravenous therapy until they improve enough to reliably absorb oral medication; those with mild disease can be treated orally from the outset.

NOTE: The above information is educational purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition.

DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.

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