Clinical profile of serologically diagnosed pneumococcal pneumonia

Objective. To describe the characteristics of serologically diagnosed pneumococcal pneumonia and compare them with those of respiratory syncytial virus (RSV) pneumonia and bacteremic pneumococcal pneumonia. Methods. IgG antibodies to pneumococcal pneumolysin and C-polysaccharide as well as immune complexes containing IgG antibodies to pneumolysin and C-polysaccharide were measured from acute and convalescent sera of 254 children with community-acquired pneumonia. Evidence of pneumococcal. infection was found in 93 children. Clinical and laboratory data were retrospectively collected from the records of 38 children with sole (all tests for 16 other microbes negative) pneumococcal pneumonia and compared with 26 sole RSV-induced pneumonia from the present series and with the data of our 85 bacteremic pneumococcal pneumonia cases reported earlier. Results. Serologically diagnosed sole pneumococcal pneumonia clinically overlapped with RSV pneumonia, but RSV pneumonia was more often associated with tachypnea (45% vs. 17%, P < 0.05) and low white blood cell counts (means, 12.0 x 10(9)/l vs. 20.8 x 10(9)/l; P < 0.001) as well as low serum C-reactive protein levels (means, 28 mg/l vs. 137 mg/l; P < 0.001). Alveolar infiltrates were found in 15% of chest radiographs of children with RSV pneumonia compared with 76% of those in children with sole pneumococcal pneumonia (P < 0.001). Patients with bacteremic pneumonia more often appeared ill (79% vs. 50%, P < 0.001) and more often had typical pneumococcal pneumonia with high fever, leukocytosis and lobar infiltrates in their chest radiographs (70% vs. 34%, P < 0.05) than those with serologically diagnosed pneumococcal pneumonia. Conclusions. Serologically detected pneumococcal pneumonia differs significantly from RSV pneumonia in laboratory and chest radiography findings, but the clinical signs and symptoms overlap considerably. Bacteremic pneumococcal pneumonia is a more severe illness than the serologically diagnosed one.