Multimorbidity in middle age predicts more subsequent hospital admissions than in older age: A nine-year retrospective cohort study of 121,188 discharged in-patients

Background: Previous research has suggested a differential short-term effect of multimorbidity on hospitalization by age, with younger groups affected more. This study compares the nine-year hospitalization pattern by age and multimorbidity status in a retrospective cohort of discharged in-patients, who represent a high-need portion of the population. Methods: We examined routine clinical records of all patients aged 45 + years with chronic conditions discharged from public general hospitals in 2005 in Hong Kong. Patterns of annual frequencies of hospital admissions and number of hospitalized days over nine years (2005-2014) were compared by multimorbidity status (1, 2, 3+ conditions) and age group (45-64, 65-74, 75 + ). Results: Among 121,188 included patients, 33.9% had 2+ conditions and 12.3% had 3 + . Hospitalization patterns varied by age and multimorbidity status. For those having only 1 condition, annual number of admissions was similar by age, but older patients had more hospitalized days (4.40 days per person-year for the 45-64 group versus 10.29 for the 75 + group in the 5th year). For those with 3+ conditions, younger patients had more admissions (4.39 admissions per person-year for the 45-64 group versus 1.87 for the 75 + group in the 5th year) but similar number of hospitalized days with older patients. Interaction analysis showed effect of multimorbidity on hospitalization was stronger in younger groups (P < 0.05). Conclusion: Middle-aged discharged in-patients with multimorbidity are admitted more often than their older counterparts and have similar total hospitalized days per year. Further research is needed to investigate chronic care needs of younger people with multimorbidity.