Differential diagnosis of viral, mycoplasmal and bacteraemic pneumococcal pneumonias on admission to hospital.

The hospital records of 150 patients with viral, mycoplasma and bacteraemic pneumococcal pneumonia were analyzed retrospectively to ascertain the discriminative value, regarding the aetiological diagnosis, of the information obtained on admission from the patient history, physical examination, simple laboratory tests and chest X-ray. With stepwise multiple discriminant analysis, the five best variables led to correct classification of 92% of bacteraemic pneumococcal, 88% of mycoplasmal, 76% of viral, and 85% of all pneumonias. Addition of a further nine variables increased the total discriminating capacity to only 89%. The best discriminating variables were the C-reactive protein determination, the presence or absence of predisposing disease or previous antibiotic treatment, the erythrocyte sedimentation rate, the presence of lymphocytosis and the band neutrophile count.