Etiological diagnosis of pneumonia in military conscripts by combined use of bacterial culture and serological methods.

The combined use of microbiological, serological and clinical laboratory methods was evaluated for etiological diagnosis of pneumonia in 106 military conscripts. Special attention was paid to rapid diagnosis of pneumococcal pneumonia and its differentiation from viral and mycoplasmal pneumonia. The microbial etiology could be established in 91 (86%) of the pneumonia patients. Pneumococcal etiology was definitely established in 32 (30%) patients and considered probable in an additional 21 patients (20%). Infection with Mycoplasma pneumoniae and adenovirus was confirmed in 23 (22%) of the patients. Mixed infections was observed in 28 (31%) of the patients with established etiology. Detection of pneumococcal antigen was the best rapid diagnostic method, being positive in 90% of the patients with purulent sputum samples in the group with a definite diagnosis of pneumococcal pneumonia prior to the start of antimicrobial treatment, while Gram stain was positive in only 65% of these patients. Sputum purulence could be used to differentiate very significantly pneumococcal from viral and mycoplasmal pneumonia (p less than 0.001). These categories of pneumonia could also be successfully differentiated by clinical laboratory tests, of which the white blood cell count and C-reactive protein were most useful. The suggested cut-off value for the cell count was 10 X 10(9)/l, and for C-reactive protein 85 mg/l. These tests could not differentiate viral from mycoplasmal pneumonias.