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Title: Effects of viral infections on upper respiratory tract bacterial colonisation in children - observational and interventional studies
Author: Thors, Valtyr Stefansson
ISNI:       0000 0004 6056 7666
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2016
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Prevalence of the common nasopharyngeal colonisers, S. pneumoniae, S. pyogenes, N. meningitidis, M. catarrhalis, H. influenzae and S. aureus depends on several factors. The aim was to explore associations between viral infections (URTI) and prevalence and density of bacteria in the nasopharynx, first in an observational cohort study (2011-12) and subsequently in a randomised, laboratory blinded intervention study (2012-13) using nasal flu vaccine (LAIV). Quantitative PCR (qPCR) assays were developed and validated to efficiently detect and quantify target organisms. 161 healthy children were recruited to the first study and 151 to the second, all attending nurseries in Bristol, UK. All had repeated nasopharyngeal swabs taken and stored in STGG broth. qPCR was used for detecting respiratory viruses and six bacterial species. t-tests and logistic regression models were used for analysis. Carriage rates of S. pneumoniae, M. catarrhalis and H. influenzae were high (78.8%, 85.7% and 85.0%, respectively) in both studies, remained stable throughout the study period and were more frequently found at higher density (>1000 gene copies/ml) in comparison with other species. Younger age was associated with higher density which was explained by more frequent respiratory viruses and nasal discharge which both were independently associated with higher bacterial density of S. pneumoniae, M. catarrhalis and H. influenzae. In the randomised controlled study, LAIV led to a delayed six-fold increase in pneumococcal density when compared to controls. Multivariable analyses showed that LAIV was also associated with increases in M. catarrhalis, H. influenzae and S. aureus density. The observed effects of LAIV provide a valuable potential tool for studying transmission of bacteria. Further studies of the biology of respiratory bacteria and viruses, including bacterial and host transcriptomics, may provide valuable information to inform vaccine design and epidemiological models to predict the indirect effects and thus overall effectiveness of both viral and bacterial vaccines.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available