Severe mental illness and infectious disease mortality: a systematic review and meta-analysis.

Background: Evidence from meta-analyses suggest that people with severe mental illness (SMI) are at increased risk of death from infectious diseases compared to those without SMI. However, few reviews have focused on mortality risk from specific infection types, apart from COVID-19. The aim of this systematic review and meta-analysis was to comprehensively describe and quantify the risk of death from infections (excluding COVID-19) in people with SMI, exploring specific infection types where possible.

Methods: PubMed, Web of Science, PsycINFO, and EMBASE were searched for relevant studies up to 18th June 2024. Studies were included if they assessed the impact of SMI (bipolar disorder, schizophrenia and schizoaffective disorders, other psychoses) on risk of mortality from any infectious disease excluding COVID-19. Random-effects meta-analyses of the risk of death from 'infectious diseases', respiratory infections, sepsis, and 'other' infections in SMI were performed. The review protocol was registered in PROSPERO (CRD42023422151).

Findings: Twenty-nine articles were included in the review. All were observational cohort studies carried out in high income countries and 59% were judged to be of good quality. Narrative analysis indicated that having SMI was associated with increased risk of death from infectious disease (23/29 studies), with mixed results for sepsis. People with SMI were more than twice as likely to die from 'infectious diseases' than the general population (pooled relative risk (RR) = 2.71, 95% confidence interval (CI) = 2.33-3.16, N = 739,852) and more than three times more likely to die from respiratory infections (pooled RR = 3.27, 95% CI = 2.57-4.17, N = 1,353,905). Sources of heterogeneity across studies included SMI diagnosis, gender, type of control group, and infection type.

Interpretation: People with SMI are at an increased risk of death from infection, particularly from respiratory infections like influenza and pneumonia and should be prioritised for preventative strategies including influenza and pneumococcal vaccines. More work is needed to fully understand why infection mortality risk is increased in SMI.

Funding: MQ Mental Health Research Fellowship MQF22∖12.