Role of viral and bacterial pathogens in causing pneumonia among Western Australian children: a case–control study protocol

Bhuiyan, Mejbah Uddin; Snelling, Thomas L; West, Rachel; Lang, Jurissa; Rahman, Tasmina; Borland, Meredith L; Thornton, Ruth; Kirkham, Lea-Ann; Sikazwe, Chisha; Martin, Andrew C; Richmond, Peter C; Smith, David W; Jaffe, Adam; Blyth, Christopher C

Although the pneumococcal conjugate vaccines have successfully reduced the hospitalization rate with CAP in children in developed countries, pneumococcus remains as an important pathogen because of emergence of non-vaccine serotypes with potential to cause severe and complicated pneumonia, and empyema [5] . With many cases being associated with respiratory viruses (Table 1) , the current immunization strategies focussing exclusively on bacterial pneumonia are expected to have modest impacts on further pneumonia case reduction. Apart from the annual influenza vaccines, to date there are no other licensed vaccine for any respiratory viruses that can be used in the community. It is critical to understand the relative contribution of specific bacterial and viral pathogens to childhood CAP, to help inform development of new therapeutics for pneumonia, including antivirals and to support ongoing efforts for new preventive strategies such as vaccines targeting RSV and parainfluenza which are in advanced stages of development. This question constitutes the primary aim of this study. Additionally, unveiling relationships between pathogen load and pathogenicity will inform tools for more accurate attribution of the infective cause of CAP, allowing better diagnosis and management of pneumonia cases using antibiotic and antiviral therapies. Finally, this study will identify emergent serotypes of pneumococcus causing CAP among vaccinated children, informing the design of future pneumococcal vaccines. [11, 15] . The Swedish study was relatively underpowered (93 x-ray confirmed cases and 240 controls) to assess attributable risk for a range of viral pathogens and in the US study, healthy controls were not enrolled contemporaneously or from all study sites which might have biased the inference for specific pathogens. The proposed study is the first case-control study of pneumonia aetiology in Australia in post-PCV vaccination era, where 250 radiologically confirmed hospitalized pneumonia cases (n=250) will be compared to 250 age-group frequency matched healthy controls for both the presence of respiratory pathogens and quantitative load of pathogens. The proposed study is expected to address the limitations from previous case-control studies through recruitment of an appropriate number of cases and controls contemporaneously and from the same study sites.