Background and objective: Atypical pneumonia occupies an important position in community-acquired pneumonia. The aim of this study was to examine whether making a diagnosis of atypical pneumonia is possible based upon the Japanese Respiratory Society guidelines.
Methods: The data from three prospective studies were reviewed. A total of 285 patients with mycoplasmal pneumonia or chlamydial pneumonia and 515 patients with pneumococcal pneumonia or Haemophilus influenzae pneumonia were assessed to determine whether these pneumonias met the diagnostic criteria for atypical pneumonia used in the Japanese Respiratory Society guidelines. The criteria were: (i) age less than 60 years; (ii) no or only minor underlying diseases; (iii) persistent cough; (iv) limited chest auscultatory findings; (v) no sputum, or no identified aetiological agent by rapid diagnosis; and (vi) a peripheral white blood cell count below 10,000/microL.
Results: All items of the criteria proved to be valid except for 'age' in patients with Chlamydophila pneumoniae pneumonia using multiple regression analysis. The sensitivity and specificity for atypical pneumonia were 77.0% and 93.0% based on four or more of the criteria respectively.
Conclusion: Pure atypical pneumonia can be differentiated to some degree by clinical symptoms and laboratory findings. It is important to differentiate and treat bacterial pneumonia and atypical pneumonia in regions such as Japan, where Streptococcus pneumoniae resistance to macrolides is high. Treatment covering the two types of pneumonia should be considered in elderly patients and those with underlying respiratory disease.