Viral bacterial co-infection of the respiratory tract during early childhood

Acute respiratory infection (ARI) is an important cause of morbidity in children. Mixed aetiology is frequent, with pathogenic viruses and bacteria co-detected in respiratory secretions. However, the clinical significance of these viral/bacterial co-infections has long been a controversial topic. While severe bacterial pneumonia following influenza infection has been well described, associations are less clear among infections caused by viruses that are more common in young children, such as respiratory syncytial virus. Although assessing the overall contribution of bacteria to disease severity is complicated by the presence of many confounding factors in clinical studies, understanding the role of viral/bacterial co-infections in defining the outcome of paediatric ARI will potentially reveal novel treatment and prevention strategies, improving patient outcomes. This review summarizes current evidence for the clinical significance of respiratory viral/bacterial co-infections in young children, discusses possible mechanisms of cooperative interaction between these pathogens and highlights areas that require further investigation.