High Density Bacterial Nasal Carriage in Children is Transient and Associated With Respiratory Viral Infections - Implications for Transmission Dynamics.

Thors, Valtyr; Christensen, Hannah; Morales-Aza, Begonia; Oliver, Elizabeth; Sikora, Paulina; Vipond, Ian; Muir, Peter; Finn, Adam

BACKGROUND This longitudinal study describes the associations between respiratory viral infections, rhinitis and the prevalence and density of the common nasopharyngeal bacterial colonisers, S. pneumoniae, M. catarrhalis, H. influenzae and S. aureus. METHODS In an observational cohort study, 161 children attending day-care-centres in Bristol, UK were recruited. Monthly nasopharyngeal swabs were taken and stored frozen in STGG broth. qPCR was used for detection of respiratory viruses and four bacterial species. T-tests and logistic regression models were used for analysis. RESULTS The frequent colonisers, S. pneumoniae(Sp), M. catarrhalis(Mc) and H. influenzae(Hi) were more frequently found at high density in contrast to S. aureus although temporally, high density carriage was short lived. Respiratory viral infections and symptoms of rhinitis were both independently and consistently associated with higher bacterial density with an observed twofold increase in density for Sp, Mc and Hi (p= 0.004 - 0.017). CONCLUSION For Sp and Hi, the association between young age and higher bacterial DNA density was explained by more frequent viral infection and increased nasal discharge while the associations between some viral species and some bacterial species' density appear to be stronger than others. Increased colonisation density and rhinitis may promote transmission of these commonly carried organisms.