GENETIC-VARIATION AMONG PNEUMOCYSTIS-CARINII HOMINIS ISOLATES IN RECURRENT PNEUMOCYSTOSIS

Pneumocystis carinii hominis is a ubiquitous organism that causes pneu monia in immunocompromised persons. Paired P. carinii hominis isolates from human immunodeficiency virus-infected persons who had two episod es of pneumocystosis were examined for genetic heterogeneity. Genetic variation was detected by sequence comparison of a portion of the mito chondrial ribosomal RNA gene, In 5 of 10 patients experiencing two epi sodes of pneumocystosis, genetically distinct isolates were associated with each episode. These included 4 of 6 patients whose second episod e of pneumocystosis occurred >6 months after their initial bout. The g enetic data support the hypothesis that some recurrent episodes of P. carinii hominis pneumonia are caused by reinfection rather than by rea ctivation of latent infection.