Are PCR assays effective in detecting pathogens associated with community-acquired pneumonia (CAP)?

Updated: Oct 31, 2019
  • Author: Stephanie L Baer, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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A 2016 study in the United Kingdom assessed the use of comprehensive molecular testing of a single lower respiratory tract specimen to detect a pathogen in CAP. [63] The study compared (1) a combination of real-time multiplex PCR assays targeting 26 different pathogens, including bacteria and viruses, with (2) culture-based diagnostic testing of the same specimens. Quantification of bacterial load was performed for 8 common bacteria, including S pneumoniae, H influenzae, and M catarrhalis. A pathogen was detected in 87% of patients with CAP using the multiplex assay, whereas culture achieved a diagnosis in only 39% of cases. Viruses were detected in 30% of cases. H influenzae and S pneumoniae were the most commonly detected bacteria. Pathogen detection was not significantly decreased when a quantitative threshold for detection of ≥105 CFU/mL for all bacterial loads was applied, although the mean bacterial load was lower in patients who had received prior antibiotics than in those who had not. Interestingly, of the 268 patients who received antibiotics prior to testing, 77.6% had a positive bacterial PCR finding, but only 32% were culture-positive. The authors concluded that comprehensive molecular testing on a lower respiratory tract specimen has the potential to positively affect targeted antibiotic therapy in most patients with CAP.

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