Variation of stroke-associated pneumonia across the United Kingdom and its impact on clinical outcomes

Abstract

Stroke associated pneumonia (SAP) occurs in 8%-14% of people admitted with a stroke. Prevalence of SAP varies considerably across the world, with various frequencies reported among registries and observational studies; however, there is no evidence explaining how SAP varies across stroke units nor what the potential reasons for this variation are. There is also no evidence suggesting how SAP variation affects clinical outcomes. This thesis aims to fill these gaps in knowledge by focusing on 4 different aspects: - to describe the variation of SAP across England and Wales and determine how much of the variation can be accounted by clinical characteristics; - to describe the relationship between SAP and specific stroke care processes in the pre-hospital, hyperacute and acute phases; - to explore the different characteristics used by clinicians to initiate antibiotics in SAP; - to explore the relationship between SAP and clinical outcomes. The first study of this thesis was a registry based cohort study that analysed SAP variation across stroke units in England and Wales, using individual patient level registry data. Median SAP prevalence was 8.5% (IQR 6.1-11.5%). SAP probability was calculated for each stroke unit, as well as variance. The mean and variance of predicted SAP probability decreased from 0.08 (0.68) to 0.05 (0.63). This suggests that patient characteristics account for 5% of the observed variation of SAP across stroke units in England and Wales. The second study of the thesis was also a registry based cohort study that analysed the relationship between timings of certain stroke care processes and the development of SAP across stroke units in England and Wales. Increased times to arrival at a stroke unit, increased time to assessment by a specialist doctor and increased time to assessment by a physiotherapist were associated with increased odds of SAP. Shorter times to thrombolysis were associated with lower odds of SAP. The third study of the thesis was a cross-sectional survey of UK stroke clinicians exploring the different characteristics and thresholds clinicians use to diagnose and initiate antibiotics for suspected SAP. It was an online survey conducted from December 2019 to February 2020. I found that clinicians use known factors such as inflammatory criteria for diagnosis and antibiotic initiation. I also found that the thresholds for each of these factors varied between clinicians, suggesting a lack of standardisation of SAP diagnosis and antibiotic initiation. The final study of the thesis was a registry based cohort study analysing the relationship between SAP and clinical outcomes. I focused on patients whose length of stay in hospital was > 7 days. By focusing on this specific population, potential confounding due to stroke severity on clinical outcomes was mitigated. SAP was consistently associated with increased risk of longer length of stay in hospital with an incidence rate ratio of 1.27 (95% CI 1.25 to 1.30), worse functional outcome at discharge with an odds ratio of 2.9 (2.9 to 3.0) and increased risk of in-hospital mortality with a hazard ratio of 1.78 (1.74 to 1.82). The work presented in this thesis has demonstrated how SAP has important variation across stroke units in England and Wales, and that there are modifiable factors that could be contributing to this observed variation. It has also confirmed the adverse association between SAP and clinical outcomes in real-world stroke unit care. This thesis is the platform for future work to develop a new intervention or tool to reduce the burden of SAP in the UK.

Date of Award	1 Aug 2022
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Andy Vail (Supervisor), Craig Smith (Supervisor) & Matthew Gittins (Supervisor)