Value of the polymerase chain reaction assay on noninvasive respiratory samples for diagnosis of community-acquired pneumonia

We studied the causes of community-acquired pneumonia (CAP) in 184 patients . Microbiologic evaluation included sputum examination, blood culture, asse ssment of acute and convalescent antibody titers for Legionella pneumophila , Mycoplasma pneumoniae, Chlamydia pneumoniae, Coxiella psitacci, Coxiella burnetii and respiratory viruses, polymerase chain reaction (PCR) assays fo r M. pneumoniae and C. pneumoniae in throat swab, and PCR assay based on th e amplification of pneumolysin gene fragment in sera. The causative pathoge n was identified in 78 patients (Streptococcus pneumoniae, 44; M. pneumonia e, 26; C. pneumoniae, 1; others, 7). S. pneumoniae was detected In serum by the PCR assay in 41 patients, five of whom also had a positive blood cultu re. PCR assay was negative in two patients with positive blood culture for S. pneumoniae. C. pneumoniae was detected by PCR In nine patients, but only one showed seroconversion. M. pneumoniae was detected by PCR in only three patients (two without seroconversion). The diagnosis of pneumonia caused b y S. pneumoniae was five times greater using PCR in serum than with blood c ulture. Detection of C. pneumoniae by PCR without fulfilling criteria for a cute infection may be considered a prior infection. The PCR assay for the d iagnosis of M. pneumoniae has a lower sensitivity than serologic methods.