Epidemiology of viral respiratory infections with focus on in-hospital influenza transmission

Sammanfattning: Human Rhinoviruses (HRV) and influenza viruses are respiratory pathogens which represent a major global disease burden. Healthcare-associated infections (HCAI) are increasingly recognized as a public health concern, but limited data has been published on the characteristics and epidemiology of HCAI caused by respiratory viruses. The aim of this thesis was to investigate the molecular epidemiology of HRV and influenza virus with special focus on in-hospital influenza transmission. In paper Ⅰ, 114 stored respiratory samples positive for HRV, collected over a four-year period, were sequenced and compared with HRV sequences identified in other parts of the world. In paper Ⅱ, a nosocomial outbreak involving 20 cases with influenza B virus infection, were retrospectively investigated by combining clinical and epidemiological data with molecular methods. In paper Ⅲ, the characteristics of 435 hospitalized adult patients with Influenza A virus infection throughout an entire year were described, whereof 114/435 (26%) were classified as HCAI. Suspected in-ward transmission was investigated by combining epidemiological investigations and whole-genome-sequencing. In paper Ⅳ, a system dynamic model for healthcare-associated influenza transmission was developed and used to identify factors promoting transmission as well as effective control interventions. Conclusions: HRV infections are represented by many subtypes. Epidemics are highly globalised, and subtypes may circulate locally for extended time periods. Influenza B may spread rapidly within an acute-care hospital, and molecular methods can be used for outbreak analysis. In-ward transmission of influenza A occurs frequently, and healthcare-associated influenza may have a severe outcome. System dynamic modelling may be a valuable tool to illustrate in-hospital transmission of influenza. Antiviral prophylaxis seemed in our model be the most effective control measure.