Radiologic diagnosis of chest infection in children: WHO end-point consolidation
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- Mahomed, N. & Madhi, S.A. Pediatr Radiol (2014) 44: 685. doi:10.1007/s00247-014-2933-0
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Pneumonia caused by Streptococcus pneumoniae is the leading cause of morbidity and mortality in children younger than 5 years, with pneumococcal conjugate vaccines providing an opportunity to reduce this burden of illness . In 2007 the World Health Organization (WHO) recommended global expansion of the 7-valent pneumococcal conjugate vaccine (PCV-7), with priority introduction in countries with a <5-years-old child mortality rate of >50/1,000 live births, in countries where >50,000 children die annually and in countries with a high prevalence of human immunodeficiency virus (HIV) .
Because radiologic diagnosis of pneumonia is used as the outcome measure in epidemiological trials, a standardized method for radiographically diagnosing pneumonia was developed by the WHO radiologic working group (initially established in 1997) to provide a consensus method for reading chest radiographs in vaccine efficacy and epidemiological trials of pneumonia . End-point consolidation was defined as a dense or fluffy opacity that occupied a portion, a lobe or an entire lung, with or without air bronchograms. Primary end-point pneumonia was defined as end-point consolidation or pleural effusion involving the lateral pleural space and associated with pulmonary parenchymal infiltrate, or an effusion that “obliterated enough of the hemithorax to obscure an opacity” .
The 9-valent pneumococcal conjugate vaccine reduced the incidence of WHO defined chest-radiograph-confirmed pneumonia by 25% in non-HIV-infected South African children  and by 37% in Gambian children . The pneumococcal conjugate vaccine (PCV) also reduced the incidence of vaccine serotype and antibiotic-resistant invasive pneumococcal disease among HIV-infected and non-HIV-infected South African children . A post hoc analysis of the South African PCV trial, however, suggested WHO radiologic end point under-estimated the burden of pneumonia prevented by vaccination . This could be attributed to the pre-determined chest radiograph end point being geared toward improved specificity, rather than sensitivity . In the United States, where the introduction of childhood pneumococcal conjugate vaccine immunization has resulted in a 36% reduction in all-cause pneumonia, many children included were unlikely to have fulfilled the WHO predetermined end point of “radiologically confirmed” pneumonia .
The current aim of the WHO is to re-establish a radiology working group with the objective of providing a more sensitive end point for radiologically confirmed pneumonia, without compromising on specificity, with which to measure vaccine effectiveness in preventing pneumonia. This would be important in future international studies evaluating the full public health benefit of immunization with pneumococcal conjugate vaccines and pneumonia epidemiological studies.
Dr. Nasreen Mahomed represented the World Federation of Pediatric Imaging at the WHO meeting to discuss the end-point criteria for pneumonia.
WHO Short and Long-term PCV Impact Evaluation meeting. Geneva, Switzerland 10-12 September 2013.
Conflict of interest