Diagnosis of pneumococcal pneumonia by polymerase chain reaction (PCR) in whole blood: a prospective clinical study

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Abstract
BACKGROUND Streptococcus pneumoniae is the leading cause of community acquired pneumonia; however, only a small proportion of cases can be detected by conventional methods. The ability of the polymerase chain reaction (PCR) test performed on whole blood samples to identify patients with pneumococcal pneumonia was investigated. METHODS One hundred and fourteen consecutive adult patients with community acquired pneumonia were evaluated by a wide battery of diagnostic tests in order to determine the aetiology. Blood samples from these patients and 50 controls were also tested by the nested PCR test to detect selected pneumolysin gene fragments of S pneumoniae. RESULTS The patients were divided into four groups: (1) 40 patients with pneumococcal pneumonia in 22 of whom (55%) the PCR was positive (eight of 11 with bacteraemia and 14 of 29 without); (2) 30 with pneumonia due to other pathogens in all of whom the PCR was negative; (3) 44 with pneumonia of unknown aetiology in 14 of whom (32%) PCR was positive, and (4) 50 controls in whom the PCR test was positive in two (4%). Thus, the sensitivity of the test was 55% and the specificity 100% (81% if positive PCR tests among undiagnosed patients are considered as false positive results). CONCLUSION PCR applied to whole blood samples appears to be a sensitive and very specific diagnostic test for identifying patients with pneumococcal pneumonia with a potential application in clinical practice.