Incidence of community acquired lower respiratory tract disease in Bristol, UK, in 2020–2024: a prospective cohort study

<h2>Summary</h2><h3>Background</h3> Surveillance of acute lower respiratory tract disease (aLRTD) is fundamental for understanding population health burden and healthcare needs. COVID-19 altered respiratory infection epidemiology, but the post-pandemic baseline incidence and severity of aLRTD remain underexplored. We describe the incidence and clinical outcomes of acute lower respiratory tract disease (aLRTD) hospitalisations in adults, stratified by clinical presentation and SARS-CoV-2 status. <h3>Methods</h3> We conducted a prospective cohort study of adults (≥18 years) admitted with signs/symptoms or diagnoses of aLRTD to two Bristol acute-care hospitals (1 August 2020–31 July 2024). Patients were classified as having pneumonia (radiological changes or clinician diagnosis, in line with the British Thoracic Society (BTS) and National Institute for Health and Care Excellence (NICE) guidance), non-pneumonic lower respiratory tract infection (NP-LRTI; signs and symptoms of infection without radiological change or pneumonia diagnosis), or no evidence of LRTI (principally chronic respiratory disease exacerbations and heart failure). The primary outcome was incidence of aLRTD, stratified by clinical presentation, age, and SARS-CoV-2 status. Secondary outcomes included 30-day mortality, hospital discharge within 30 days, hospital length of stay, Intensive Care Unit (ICU) admission, ICU length of stay, and 1-year mortality. Population denominators were calculated using General Practitioner (GP) registration data linked to hospital admission patterns. <h3>Findings</h3> Among 457,112 hospitalisations, 44,766 were attributed to aLRTD (96% with consented data available): 20,639 pneumonia (48.2%), 15,061 NP-LRTI (35.2%), and 7134 no evidence of LRTI (16.7%). Overall, aLRTD incidence peaked in Year 2 (Aug 2021–Jul 2022) at 14.4/1000 person-years, driven primarily by COVID-19 cases, before stabilising around 13.6/1000 in Year 4 (Aug 2023–Jul 2024). SARS-CoV-2 pneumonia decreased from 2.6 in Year 2 to 0.9/1000 in Year 4, while non-COVID pneumonia remained stable (3.6–5.5/1000) between Year 2 and 4. Compared to pneumonia, NP-LRTI (HR 0.32, 95% CI: 0.29–0.35) and no evidence of LRTI (HR 0.43, 95% CI: 0.19–0.97) had lower mortality risk. Age ≥85 years (HR 5.1, 95% CI: 2.8–9.5, compared with 18–64 years) and severe comorbidities (HR 3.4, 95% CI: 2.8–4.1, compared with none) were associated with increased risk of 30-day mortality. <h3>Interpretation</h3> XXaLRTD incidence and severity remained substantial throughout and after COVID-19, with non-COVID infections maintaining consistent rates despite public health measures. These findings highlight the persistent burden of hospitalisations for aLRTD, measured in incidence and adverse outcomes and the importance of comprehensive aLRTD surveillance for public health planning. <h3>Funding</h3> AvonCAP is an investigator-led project funded under a collaborative agreement by Pfizer.