Standardizing Surveillance of Pneumococcal Disease

Background: Surveillance for invasive pneumococcal disease has been conducted using a variety of case ascertainment methods and diagnostic tools. Interstudy differences in observed rates of invasive pneumococcal disease could reflect variations in surveillance methods or true epidemiological differences in disease incidence. To facilitate comparisons of surveillance data among countries, investigators of Pneumococcal Vaccines Accelerated Development and Introduction Plan-sponsored projects have developed standard case definitions and data reporting methods.

Methods: Investigators developed case definitions for meningitis, pneumonia, and very severe disease using existing World Health Organization guidelines and clinical definitions from Africa and Asia. Standardized case definitions were used to standardize reporting of aggregated results. Univariate analyses were conducted to compare results among countries and to identify factors contributing to detection of Streptococcus pneumoniae.

Results: Surveillance sites varied with regard to the age groups targeted, disease syndromes monitored, specimens collected, and laboratory methods employed. The proportion of specimens positive for pneumococcus was greater for cerebrospinal fluid specimens (1.2%-19.4%) than for blood specimens (0.1%-1.4%) in all countries (range, 1.3-38-fold greater). The distribution of disease syndromes and pneumonia severity captured by surveillance differed among countries. The proportion of disease cases with pneumococcus detected varied by syndrome (meningitis, 1.4%-10.8%; pneumonia, 0.2%-1.3%; other, 0.2%-1.2%) and illness severity (nonsevere pneumonia, 0%-2.7%; severe pneumonia, 0.2%-1.2%), although these variations were not consistent for all sites. Antigen testing and polymerase chain reaction increased the proportion of cerebrospinal fluid specimens with pneumococcus identified by 1.3-5.5-fold, compared with culture alone.

Conclusions: Standardized case definitions and data reporting enhanced our understanding of pneumococcal epidemiology and enabled us to assess the contributions of specimen type, disease syndrome, pneumonia severity, and diagnostic tools to rate of pneumococcal detection. Broader standardization and more-detailed data reporting would further improve interpretation of surveillance results.