Is it possible to distinguish between atypical pneumonia and bacterial pneumonia?: evaluation of the guidelines for community-acquired pneumonia in Japan.

The Japanese Respiratory Society (JRS) published the guidelines for the management of community-acquired pneumonia in 2000. The guidelines set up nine parameters and criteria for the differential diagnosis of atypical pneumonia and bacterial pneumonia based on clinical symptoms, physical signs and laboratory data. To evaluate the performance of these guideline criteria, 91 cases of Chlamydia pneumoniae (53 cases were pure-C. pneumoniae and 38 cases were mixed-C. pneumoniae pneumonia), 103 cases of Mycoplasma pneumoniae (86 cases were pure-M. pneumoniae and 17 cases were mixed-M. pneumoniae pneumonia) and 144 cases of bacterial (Streptococcus pneumoniae and/or Haemophilus influenzae) pneumonia were analyzed. The accordance rate for a suspected atypical pneumonia with the guideline criteria was 84.8% for pure-M. pneumoniae pneumonia and 60.3% for pure-C. pneumoniae pneumonia, but only 9.0% for bacterial pneumonia, 12.1% for mixed-C. pneumoniae pneumonia and 16.6% for mixed-M. pneumoniae pneumonia. Overall, the sensitivity and specificity of the criteria in the JRS guidelines were 75.5% and 90.9%, respectively. Our results indicated that the differentiation of pneumonia in the JRS guidelines is useful for the diagnosis of M. pneumoniae pneumonia, but difficult to apply to the diagnosis of C. pneumoniae pneumonia.