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1. Introduction
Pneumonia remains the most important cause of mortality and morbidity in young children globally [1,2]. In addition to the impact of acute disease, respiratory infections (especially when repeated) in young children are associated with long-term lung function abnormality and disease in adults [3]. Early diagnosis and management are critical to short- and long-term health outcomes with several clinical guidelines now available for both developing and developed country settings, albeit with concerns about the inconsistencies between these documents [4]. The implementation and effectiveness of the guidelines vary widely within and between countries and, in many regions, improvements are still required in the diagnosis and management of pneumonia at the community level [5–9].
Despite the commonality of pneumonia in children, disagreement remains about diagnosis in both clinical and research settings [9,10]. Many factors contribute to these differences, including: health systems resourcing, the number of possible causative micro-organisms, host and environmental factors, timing of presentation to a health service, expertise of the health service providers at various levels of the health care system, availability of diagnostic facilities and the absence of a true diagnostic gold standard [11,12]. The World Health Organization (WHO) clinical definition developed for the community setting in developing countries is based on the presence of cough and tachypnoea [13]. This definition was developed particularly with the intention of identifying children who had bacterial pneumonia and required antibiotics [14]. However, while highly sensitive, this definition lacks specificity. The major reason for this is the problem of viral infections affecting airways but not lung parenchyma in children with these infections [15], although many of these children may have co-infection particularly with Streptococcus pneumoniae [16]. In addition, in settings where there is a high prevalence of conditions with similar symptoms and signs like malaria and tuberculosis (TB), differentiating pneumonia from malaria [17,18] and TB (with human immunodeficiency virus) at the time of presentation may be difficult [18,19]. Pneumonia may also be masked in cases of severe diarrhoea and hypokalaemia [20].
In the appropriate setting (e.g. trained health care professionals and diagnostic services), other factors may be considered to improve the specificity of the diagnosis of pneumonia. These factors include clinical symptoms and signs (e.g. crackles) and objective tests (e.g. pulse oximetry and radiology). The microbiological cause...