Five-decade prevalence of delirium in pneumonia, risk factors and associated mortality: a systematic review and meta-analysis

Delirium can occur in patients with pneumonia, but its prevalence is inconsistent across studies. Unreliable estimates and uncertainty regarding the significance of patient-specific versus microbiological risk factors hinder delirium management and prognosis. Here, we provide robust estimates of delirium prevalence in patients with pneumonia, associated risk factors and association with mortality.

Methods

We searched five databases (Medline, Cochrane Library, Embase, PsycINFO and Scopus), from inception to 6 August 2024. We included studies in adults hospitalised with pneumonia reporting delirium, encephalopathy or altered mental status. Two investigators extracted data and assessed risk of bias. Summary rates were calculated using random-effects models. We performed prespecified analyses for diagnostic methods, microbiologic factors, clinical factors and mortality, with sensitivity analysis among studies at low risk of bias. The review protocol was registered with PROSPERO: CRD42023385571.

Results

Delirium prevalence across 126 studies was 22% (95% CI 18–26%) and higher in studies at low risk of bias (40%, 95% CI 24%–58%; n=11). Standardised assessments yielded higher rates than symptom- or International Classification of Diseases code-based assessments (p<0.05). Surprisingly, delirium rates did not differ by microbiological aetiology (p = 0.63), including COVID-19, nor by pneumonia origin (p=0.14). Predisposing factors included older age and neurologic and systemic comorbidities. Delirium was associated with increased mortality (odds ratio 4.3, 95% CI 3.24–5.76; p<0.001), without change over five decades (p=0.32).

Interpretation

Delirium is highly prevalent and enduring in pneumonia, with nearly double the estimated prevalence when standardised diagnostic methods for both pneumonia and delirium are used. Our results emphasise patient- and care-related factors over microbiological causes, including COVID-19. Delirium's entrenched association with mortality, even considering covariates, reinforces the need to manage delirium as a convergent syndrome in pneumonia.