A study on epidemiological trends in community acquired pneumonia and associated outcomes in the UK

Background Community acquired pneumonia (CAP) is a common illness in patients admitted to hospital, accounting for nearly 10% of acute medical admissions. Despite widespread use of antimicrobial therapy, morbidity and mortality from this disease remains high. In recent years in the UK, there have been significant developments in both preventative and treatment strategies for this illness. To understand the impact of these changes and direct future management strategies, it is important that the epidemiology of this disease is fully understood. This thesis investigates changes in epidemiology and outcomes in adult patients admitted to UK hospitals with a primary diagnosis of CAP, in recent years and with reference to the herd protection effect of the conjugate Streptococcus pneumoniae vaccine. Methods There are 3 study populations presented in this thesis. Data were derived from (a) the British Thoracic Society national CAP audit database, (b) a longitudinal cohort study of adults hospitalised with CAP, within the Greater Nottingham area, and (c) an observational study of adults admitted to four hospitals within the East Midlands area with a diagnosis of CAP. The specific methods used for the identification of study participants, laboratory and statistical analysis are described in detail in ensuing chapters. Results Across the UK, there was a significant reduction in 30-day mortality between 2009 and 2014; this improvement in outcome may be attributable in some part to improved processes of care. Whilst data derived from coding databases have previously been used to report CAP related mortality trends, this thesis has demonstrated significant variation in coding accuracy across UK institutions and that miscoded cases of pneumonia had lower odds of 30 day mortality compared to those individuals with CAP. Consequent to herd effects from national infant vaccination programmes and changes in nasopharyngeal carriage of S pneumoniae, this thesis shows that (a) school holiday periods were associated with increased incidence of pneumococcal CAP in hospitalised adults, (b) older adults at high risk of pneumococcal disease were less likely to be hospitalised with vaccine serotype CAP compared to non-vaccine-serotype pneumococcal CAP, and (c) there was a decrease in the overall burden of vaccine-serotype pneumococcal CAP compared to non-vaccine-serotype pneumococcal CAP. Conclusion Important changes in the epidemiology of adult CAP in the UK over recent years are reported in this thesis. This includes temporal decreases in mortality rates of all cause CAP, as well as a significant ongoing burden of non-vaccine serotype pneumococcal CAP. This data on the current burden of disease and associated outcomes should help inform future CAP management strategies