Pneumocystis carinii infection clinical features and diagnosis

Pneumocystis carinii infection clinical features and diagnosis

Pneumocystis carinii is a common organism that is foundworldwide. Although previously classified as a protozoan,evidence suggests that it may be fungal in nature. It infectsthe lungs and causes no problems in normal human hosts.The organism is found in autopsy material from healthypeople in up to 4% of cases, and serological studies inEurope have shown up to 75% seropositivity in healthychildren. The reservoirs of infection and the mode of transmissionare poorly defined, but it seems likely that personto-person droplet infection occurs.It causes interstitial pneumonitis in premature andyoung infants, in children with protein-energy malnutrition,in immunosuppressed patients during treatment forhaematological malignancies, and in AIDS patients in thewest. It is uncommon in AIDS in Africa.In normal lung the organisms are found singly or in clusterson the alveolar septal wall, with no surrounding hostresponse. When there is pneumonitis large numbers ofparasites are found in the alveoli, with desquamationof alveolar cells and accumulation of proteinaceousmaterial in the alveolar spaces.Clinical features and diagnosisThe clinical features of Pn. carinii pneumonia are progressivedyspnoea, cough, fever and weight loss. Chestexamination is often normal; chest radiographs may benormal initially but progress fairly rapidly to show extensive interstitial shadowing. The diagnosis should be suspectedin immunosuppressed patients, especially thosewith AIDS, and confirmation is obtained from examinationof bronchial washings obtained at bronchoscopy or insputum induced using nebulized hypertonic saline.ManagementThe treatment is adequate oxygenation and ventilatorysupport when necessary, and chemotherapy with eitherhigh-dose co-trimoxazole (four tablets four times a day) orpentamidine given by intramuscular injection or slow intravenousinfusion in 250 mL of normal saline or 5% dextroseover 1-2 hours. Corticosteroids are added in moderate orsevere cases. Fever, rash and leukopenia have been seen inAIDS patients after about 7-10 days on co-trimoxazole, anda change to pentamidine may be necessary, as treatment forat least 21 days is required. Pentamidine side-effects includerenal and hepatic failure and prolonged hypoglycaemia.There is a 20% mortality in AIDS patients in their firstepisode of Pn. carinii, irrespective of treatment. Prophylaxiswith co-trimoxazole for this infection has been effectivein patients with acute leukaemia. Primary prophylaxis inAIDS patients with the combination of an antifolate anda sulphonamide/sulphone is of value, and nebulized pentamidinehas also been used successfully.

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