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The development and availability of improved vaccines, particularly the pneumococcal (PCV) and Haemophilus influenzae type b (Hib) conjugate vaccines have substantially reduced the incidence of childhood pneumonia and severe pneumonia associated with these pathogens over the last decade.1 However, despite a declining pneumonia incidence and high rates of immunisation, pneumonia remains the leading cause of childhood mortality globally and a major cause of hospitalisation.2
Defining the aetiology of pneumonia has become crucial to develop appropriate management strategies, and guide development of new vaccines. Further, the development of better methods for specimen collection and of molecular diagnostics has provided more sensitive techniques to define potential aetiological agents.3 However, assigning aetiology may be challenging as it can be difficult to distinguish colonising from pathogenic organisms in respiratory specimens, blood culture rarely is positive and pneumonia, especially severe disease, may frequently be due to multiple copathogens.
In this issue of Thorax, Rhedin and colleagues report the association of viral pathogens and radiological pneumonia in Swedish children (median age 21 months) using a matched case–control study conducted over three winter seasons.4 PCV immunisation was well established before the study began. Healthy control children were randomly selected during routine visits; aetiological diagnosis was investigated using a quantitative PCR assay for 15 viruses performed on nasopharyngeal aspirates. There are several notable findings. First, viruses were detected in >80% of cases and in approximately 60% of controls. Second, in multivariate analysis, respiratory syncytial virus (RSV) (adjusted OR (aOR) 21.3), influenza virus (aOR 13.8) or human metapneumovirus (hMPV) (aOR 14.9) were most strongly associated with pneumonia, with RSV being most commonly detected. …