Improvement of pneumococcal pneumonia diagnostics by the use of rt-PCR on plasma and respiratory samples

Abstract

Background: The aim of the study was to assess the performance of a real-time polymerase chain reaction (rt-PCR) assay on plasma and respiratory samples for the diagnosis of pneumococcal pneumonia.

Methods: Three hundred and forty patients (160 children and 180 adults) with community-acquired pneumonia were included prospectively from January 2011 to May 2012. Blood samples were obtained simultaneously for culture and rt-PCR targeting the lytA gene. Respiratory samples were also obtained: nasopharyngeal swab in nearly all patients and sputum or tracheal aspirate when available.

Results: Streptococcus pneumoniae was detected in 222 (65%) of 340 patients: 143 (89%) children and 79 (44%) adults. Pneumonia was assigned as definite pneumococcal in 96 (28.2%) of 340 patients, according to S. pneumoniae detected in blood: in 54 (33.8%) children – by rt-PCR in 51 (31.9%) and by culture in 5 (3.1%); and in 42 (23.3%) adults – by rt-PCR in 41 (22.8%) and by culture in 12 (6.7%). Pneumonia was considered as probably pneumococcal in 19 (10.6%) adults according to S. pneumoniae detected in sputum/tracheal aspirate, by rt-PCR in 19 and by culture in 5. In 18 adults and 89 children with S. pneumoniae detected only in the nasopharynx, pneumonia was considered as possibly pneumococcal; however it should be noted that nasopharyngeal colonization with S. pneumoniae is also common in children with other aetiologies of pneumonia.

Conclusions: rt-PCR on plasma and other samples performed significantly better than culture for the detection of pneumococcal pneumonia (p < 0.0005) in children and adults.

Keywords::

• Pneumococcal pneumonia
• children and adults
• culture
• rt-PCR
• blood and respiratory samples

Acknowledgements

We are grateful to the staff of the Department of Infectious Diseases, University Medical Centre Ljubljana for specimen collection, and the staff of the Institute of Microbiology and Immunology, Faculty of Medicine, for laboratory assistance.

Declaration of interest: No funding received; no conflicts of interest.