Source of Pneumocystis carinii in recurrent episodes of pneumonia in AIDS patients

Objective: To investigate the hypothesis that P. carinii special form hominis(P.c hominis) reinfections occur in AIDS patients. Design: Polymerase chain reaction (PCR) was used to identify patients who had different P.c. hominis mitochondrial DNA (mtrRNA) genotypes in the two disease episodes (genotype switching). P.c. hominis from these patients were analysed with an allele-specific PCR (ASP) assay to determine whether the genotype found in a second disease episode were present in the first disease episode. To assess the possible contributions of other factors to genotype switching, data on the sampling method and drugs used to treat each patient were compiled. Methods: Bronchoalveolar lavage fluid (BALF) was subjected to PCR using primers that amplified a 346 base-pair region of the mtrRNA locus known to be polymorphic at site 85 of the amplicon. Samples from patients in whom the P.c, hominis mtrRNA sequence had changed at site 85 in the two disease episodes were studied by ASP in which primers designed to prime synthesis from the allele of the mtrRNA sequence found in second episodes of disease were used in PCR of P.c. hominis DNA from first episodes of P. carinii pneumonia. Results: In four of five patients who produced P.c. hominis with different mtrRNA genotypes during first and second episodes, ASP did not detect the second-episode genotype in first-episode BALF. There was no evidence that either sampling methods or drug-resistance contributed to genotype switching. Conclusions: P.c. hominis reinfections occur in AIDS patients.