Diagnosis of Pneumocystis jirovecii pneumonia by detection of DNA in blood and oropharyngeal wash, compared with sputum

Objectives Molecular diagnostic methods on lower respiratory specimens for Pneumocystis pneumonia (PCP) are recommended, but specimens can be difficult to obtain. This study examined the diagnostic utility of PCP PCR (polymerase chain reaction) on oropharyngeal wash (OPW) and blood vs. sputum (spontaneous and induced) to find faster, simpler and less invasive diagnostic methods. Methods We prospectively recruited consenting adults with symptoms consistent with PCP. Real-time PCR targeted the Pneumocystis mitochondrial large subunit ribosomal RNA gene, using the aforementioned specimens. Clinical data were collected from routine records. Results 45 participants provided 45 sputa, 31 OPW and 41 blood samples. Median age was 39 years and 41 (91%) were male, with median CD4 count 64 cells/µL. Sputum PCR was positive in 27/45 (60%). Comparative sensitivity of OPW was 9/19 (47%, 95% confidence interval [CI] 23, 71) and blood 12/24 (50%, 95% CI 29, 71), both with specificity 100%. Including only samples obtained <=2 days after treatment start, sensitivity of OPW was 80% (8/10, 95% CI 51, 100); blood 57% (8/14, 95% CI 29, 86) and combined tests 88% (14/16, 95% CI 70,100). In 14/16 individuals with PCP and specimens <=2 days after treatment start, diagnosis was possible using non-respiratory samples. Conclusions Despite moderate sensitivity of individual tests, combined PCP PCR on early blood and OPW specimens had high sensitivity and could reduce need for invasive procedures. There were no false-positive results on non-respiratory samples. Sampling and laboratory methods use technology frequently employed in this patient group and so require few additional resources.