Age and co-morbidities as independent risk factors of infections leading to hospital admission in the last year of life among the elderly: A retrospective registry-based study.

Background: The immune system declines with age, but the impact of chronological age may be affected by sex, co-morbidities, and sociodemographic factors. Objective: The article aims to study infections associated with hospital admission in the elderly in their last year of life and the impact of age, sex, co-morbidities, and sociodemographic factors. Method: A retrospective study based on registry data covering all care visits in Stockholm Region, Sweden, for 7 years was conducted. All deceased subjects with at least one hospital admission with infection as the main diagnosis in the last year of life were compared with subjects with no such admission. Subjects were categorized into three different age-groups 65-79, 80-89, and 90 years and above. Co-morbidity was measured by the Charlson Comorbidity Index (CCI) and sociodemographic factors were assessed using the 'Mosaic-system'. Subjects living in nursing homes were analyzed separately. Uni- and multivariable logistic regressions were conducted. Results: Of the 55,238 subjects in the study population, 14,192 (26%) had at least one hospital admission due to infection in the last year of life. The risk of having a severe infection increased with age, adjusted odds ratio (OR): 1.30 (1.25-1.36), and 1.60 (1.52-1.69) for the age-groups 80-89 and ≥ 90 compared to the age-group 65-79. The most important factor for infection was a high co-morbidity score; adjusted OR: 1.75 (1.68-1.82). Male sex and living in a less affluent area were weaker risk factors for infections. Conclusion: Chronological age and co-morbidities are independent risk factors of infections associated with hospital admission in the last year in life while male sex and sociodemographic factors have less impact.