Describing the epidemiology and aetiology of bacterial pneumonia in children: an unresolved problem.

Abstract

Acute lower respiratory infections are among the most common problems in children worldwide. In developing countries, they constitute the most common cause of mortality in children aged less than five years, leading to an estimated 1.9 million deaths annually, most of which are thought to be due to pneumonia (1). Despite the frequency and severity of this condition, the burden and epidemiology of disease have been difficult to describe with sufficient accuracy because of the lack of an adequate definition of pneumonia for epidemiological purposes and of the lack of sensitive and specific tests to establish bacterial aetiology. Some of these problems, which still remain unresolved, are evident in the study reported by Nacul et al. in this issue of the Journal (2). Defining pneumonia Conventionally, pneumonia is clinically diagnosed based on a combination of clinical signs and symptoms and confirmed by findings of chest radiography. Simple clinical signs, such as tachypnoea and lower chest in-drawing, have been shown to be reliable signs of pneumonia (3). While these signs are appropriate for case management in primary healthcare programmes where high sensitivity is important, they are not sufficiently specific to accurately estimate the burden of disease and give low efficacy estimates for interventions that are aimed specifically at preventing bacterial pneumonia. Auscultatory findings, such as crepitations and bronchial breath sounds, have been conventionally used by physicians in the clinical diagnosis of pneumonia. However, these findings are subjective and highly dependent on the skill of the observer. As a result, the diagnosis of pneumonia using auscultatory findings has been difficult to standardize, and inter-observer agreement regarding the presence and absence of these signs has been poor (4). Radiography is considered to be the gold standard for the diagnosis of pneumonia. However, different studies have varied in the radiological findings used to define pneumonia. While some studies have classified only cases with alveolar consolidation as pneumonia, others have considered the presence of any pulmonary parenchymal infiltrates as constituting pneumonia. Furthermore, there is relatively poor agreement even between radiologists on the presence or absence of infiltrates in paediatric chest radiographs. This variability persists even when standard definitions and reporting forms are used. Analysis of the readings of four trained paediatric radiologists who read chest radiographs from two different studies using common definitions and reporting forms showed that while there was reasonable agreement for alveolar consolidation, agreement was low for many other findings (Weber M. Personal communication, 2004). Despite these limitations, radiography still remains the best available tool to diagnose pneumonia. Since bacterial pneumonia is thought to account for the majority of pneumonia-related deaths and since current interventions, such as vaccines and case management, focus on bacterial disease, the World Health Organization (WHO) initiated a process to improve the interobserver agreement for categorizing pneumonia with alveolar consolidation, the finding that is most representative of this condition. Asimplified definition, coupled with a training programme, and the system of two independent readings with an arbitration reading of those images where the two primary readings were discordant, was developed and tested (5). The use of the definitions and methods resulted in reasonably good agreement in categorizing pneumonia with alveolar consolidation and has been used in Haemophilus influenzae type b (Hib) and pneumococcal vaccine trials to determine the effect of these vaccines on pneumonia (6). The same definitions are also currently being used for documenting the burden of pneumonia in several studies in developing countries. Available data suggest that, while the radiological definitions of WHO are enriched for the diagnosis of bacterial pneumonia, they are still not optimally sensitive and specific (7-12). …