Pneumococcal serology in children's respiratory infections

The role of Streptococcus pneumoniae in the etiology of respiratory tract infections has been studied serologically using microbe-specific antibody and immune complex assays. Serological methods are sensitive in the bacteremic pneumococcal pneumonia of adults. In children, however, pneumococcal pneumonia is seldom bacteremic, and, thus, in the absence of a gold standard for the detection of pneumococcal infection, serological methods are still insufficiently validated. We report here indirect evidence for the sensitivity and specificity of pneumococcal serology in children. Serological evidence of pneumococcal infection has been found in 27% to 38% of children with radiologically confirmed pneumonia, in 7% to 8% of children with viral wheezy bronchitis, and in <1% to 5% of children and young adults with viral upper respiratory infection. Serological findings for pneumococcal infection have been dependent on the study venue, whether in hospital or ambulatory subjects, and on the test panel used. Where both antibody and immune complex assays have been available, the proportion of children with pneumococcal infection has been 32% to 37% in inpatients and 27% to 28% in outpatients. The respective rates have been 10% to 18% by antibody assays alone. Pneumococcal acute otitis media, when present with pneumonia, may confound findings in pneumococcal serology, but pure nasopharyngeal carriage of S. pneumoniae has little effect. In contrast, carriage acquisition of a new serotype may induce significant antibody production. Thus, understandably, significant rises between paired sera in antibodies to pneumococcal capsular polysaccharides and pneumococcal pneumolysin have been found in <1% to 3% of non-symptomatic children and young adults. Findings from the last 20 years indirectly suggest that pneumococcal antibody and immune complex assays are sensitive and specific enough for the detection of pneumococcal infection in children. However, the methods are too complex for routine clinical practice, and, so far, serological methods for S. pneumoniae infections have only been used for research purposes.