The purpose of this study is to investigate the relationship between viral infections of the upper respiratory tract, perturbations of the nasopharyngeal microbiome in children, and the risk of acute bacterial sinusitis over a one year period. The investigators will determine the incidence of acute bacterial sinusitis post viral upper respiratory infection and identify the viral antecedent infections and other risk factors which predispose to infection and ultimately design strategies to reduce the burden of disease and antimicrobial resistance.