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Pneumocystis jirovecii 

Pneumocystis jirovecii

Pneumocystis jirovecii

Robert F. Miller

and Laurence Huang


July 30, 2015: This chapter has been re-evaluated and remains up-to-date. No changes have been necessary.


Early initiation of antiretroviral therapy associated with reduced mortality in HIV-infected patients presenting with opportunistic infections.

Updated on 31 May 2012. The previous version of this content can be found here.
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date: 28 April 2017

The ascomycete fungus Pneumocystis jirovecii (previously called Pneumocystis carinii) is the cause of pneumocystis pneumonia (PCP) in humans, which occurs largely among people with impaired CD4+ T-lymphocyte function or numbers, e.g those infected with HIV, or organ transplant recipients taking therapeutic immunosuppressive agents. The organism is restricted to humans, and disease is now thought to arise from de novo infection by inhalation from an exogenous source.

Clinical features and diagnosis—presentation of PCP is nonspecific, with progressive dyspnoea and nonproductive cough. Examination of the chest is typically normal, but fine bibasal end-inspiratory crackles may be heard. Diagnosis is usually by demonstration of organisms on microscopy (preferably with immunofluorescence staining) of induced sputum or bronchoalveolar lavage fluid.

Treatment and prognosis—aside from supportive care, first-line therapy of PCP is sulphamethoxazole–trimethoprim (co-trimoxazole, which has a high rate of treatment-limiting adverse drug reactions), with adjunctive corticosteroids indicated for those with severe disease. In patients whose disease is failing to respond, or those intolerant of co-trimoxazole, the main alternatives are intravenous pentamidine or clindamycin with primaquine. Among HIV-infected patients, recent data suggest that early initiation of antiretroviral therapy is beneficial.

Prevention—primary prophylaxis is recommended for (1) HIV-infected patients—when the CD4 count falls below 200 cells/µl or they have HIV-constitutional features or other AIDS-defining diagnoses; and (2) other at risk groups—e.g. some organ transplant recipients. Secondary prophylaxis is given after an episode of PCP. The first-choice prophylactic agent is co-trimoxazole; alternative options include nebulized pentamidine.

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