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Clinical and Diagnostic Laboratory Immunology, October 2005, p. 1195-1201, Vol. 12, No. 10
1071-412X/05/$08.00+0     doi:10.1128/CDLI.12.10.1195-1201.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Diagnosis of Invasive Pneumococcal Disease among Children in Kenya with Enzyme-Linked Immunosorbent Assay for Immunoglobulin G Antibodies to Pneumococcal Surface Adhesin A

J. Anthony G. Scott,1,2* Zena Mlacha,1 Joyce Nyiro,1 Salome Njenga,1 Pole Lewa,1 Jacktone Obiero,1 Hanningtone Otieno,1 Jacquelyn S. Sampson,3 and George M. Carlone3

Wellcome Trust/Kenya Medical Research Institute, Centre for Geographic Medicine Research—Coast, Kilifi, Kenya,1 Nuffield Department of Clinical Medicine, Oxford University, John Radcliffe Hospital, Oxford, United Kingdom,2 Respiratory Diseases Immunology Laboratory, National Center for Infectious Diseases, Centers for Disease Control and Prevention, 1600 Clifton Road NE, Atlanta, Georgia 303333

Received 25 April 2005/ Returned for modification 29 July 2005/ Accepted 11 August 2005

Diagnostic techniques for invasive pneumococcal disease (IPD) in children are insensitive and underestimate both the burden of disease and the cost-effectiveness of pneumococcal conjugate vaccination (PCV). Consequently, there is little demand for the highly effective PCV outside the United States and Europe. In Kenya, diagnosis of pneumococcal pneumonia in adults was achieved with a sensitivity of 0.70 and a specificity of 0.98 using enzyme-linked immunosorbent assays (ELISAs) of paired plasma samples for immunoglobulin G (IgG) to pneumococcal surface adhesin A (PsaA). We aimed to validate the same technique in children. We assayed paired blood samples from 98 children with IPD, 95 age-matched children with malaria/anemia, and 97 age-matched healthy controls by using an ELISA for anti-PsaA IgG. Sensitivity and specificity were determined in IPD patients and healthy controls. Specificity (0.97; 95% confidence interval [CI], 0.91 to 0.99) and sensitivity (0.42; 95% CI, 0.32 to 0.52) were optimized at a 2.7-fold rise in anti-PsaA antibody concentration. Sensitivity was improved to a maximum of 0.50 by restricting testing to children of <2 years old, by excluding IPD patients who were not sampled on the first day of presentation, and by incorporating high existing antibody concentrations in the analysis. Assay performance was independent of nasopharyngeal carriage of pneumococci at recruitment. This assay improves on existing diagnostic tools for IPD in children but would still leave over half of all cases undetected in epidemiological studies. Effective diagnosis of pneumococcal disease in children is urgently required but poorly served by existing technology.

* Corresponding author. Mailing address: Wellcome Trust/KEMRI Centre for Geographic Medicine Research—Coast, P. O. Box 230, Kilifi, Kenya. Phone: 254 415 25453. Fax: 254 415 22390. E-mail: ascott{at}ikilifi.net.

Clinical and Diagnostic Laboratory Immunology, October 2005, p. 1195-1201, Vol. 12, No. 10
1071-412X/05/$08.00+0     doi:10.1128/CDLI.12.10.1195-1201.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.





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