Epidemiology of coinfection and antimicrobial use in populations with influenza or SARS-CoV-2 associated admissions in Scotland to inform targeted ant

Microbiologically confirmed bacterial co-infections (48 hours of admission) are identified in up to 23% patients with hospitalised influenza (flu), and is associated with increased morbidity and mortality.1 The most common organisms complicating influenza infection are Streptococcus pneumoniae and Staphylococcus aureus.1 In contrast, the prevalence of bacterial co-infection is much lower (~6%) in hospitalised patients with COVID-19,2 in whom Staphylococcus aureus, Haemophilus influenzae and Escherichia coli are the most frequently identified organisms.3 Despite this knowledge, our recent work demonstrated that a high proportion of patients with COVID-19 were prescribed with antimicrobials in the 2022/23 winter season, and the proportion did not significantly differ from patients with influenza infection (70% vs. 62%; Ho, personal communications). Over-prescription of antimicrobials not only leads to an increasing prevalence of resistant bacteria, it also increases the risk of Clostridioides difficile infection which causes significant morbidity and mortality, particularly in vulnerable patients. It is estimated that antimicrobial resistance (AMR) contributes to ~700,000 deaths globally each year.4 Concerningly, experiential evidence suggests that antimicrobial stewardship programmes, which serve to optimise antimicrobial use and minimise the spread and impact of AMR, have been significantly disrupted by COVID-19. Respiratory virus-associated acute respiratory infections contribute a high proportion of hospital admissions in the UK, particularly in winter. Since flu and SARS-CoV-2 are expected to cocirculate from hereon, and the prevalence and aetiology of bacterial co-infection differ between patients admitted with influenza infection or COVID-19, there is an opportunity to augment antimicrobial stewardship by developing a streamlined management pathway, with differing thresholds to prescribe empirical antimicrobials in patients with severe influenza or COVID-19, and tailoring the choice of empirical antimicrobials based on viral aetiology and/or underlying health conditions. This requires up-to-date data on the epidemiology of bacterial coinfections associated with influenza- and COVID-19-related hospital admissions, in addition to current antimicrobial use in the peri- and post-pandemic period. Furthermore, as clinical signs, chest X-ray findings and commonly used biomarkers, such as C-reactive protein (CRP) and procalcitonin, discriminate poorly for bacterial co-infection in COVID-19, we aim to identify potential biomarker(s) that may aid stratification of hospitalised flu or COVID-19 patients by co-infection status. Our primary aim is to characterise the epidemiology of coinfection and antimicrobial prescription in individuals with influenza or SARS-CoV-2-associated hospitalisation in Scotland, by using Scotland-wide national surveillance dataset.