Association of in-hospital multimorbidity with healthcare outcomes in Swiss medical inpatients.

Importance: Multimorbidity poses a worldwide health- and socio-economic challenge, exacerbated by changing demographics. The association of multimorbidity with healthcare outcomes in hospitalised medical inpatients remains incompletely understood.

Objective: To examine the prevalence and burden of in-hospital multimorbidity over a 6-year time period and its association with in-hospital mortality, intensive care unit admission, length of hospital stay and readmission rates.

Design: This cross-sectional study analysed Swiss hospital discharge records from 1 January 2012 to 31 December 2017.

Setting: The study used population-based, administrative data from the Swiss Federal Statistical Office to investigate all adult medical cases in Switzerland.

Participants: 2,220,000 population-based medical discharge records from 1,463,781 anonymised patients were included in the analysis. Multimorbidity was defined according to the World Health Organization as the presence of at least two chronic conditions. We applied the “Chronic Condition Indicator for the International Classification of Diseases (ICD-10-CM)”, which divides all ICD-10 codes into chronic and acute conditions, to define the number of chronic conditions.

Main Measures: Time- and age-stratified prevalence of multimorbidity and its association with in-hospital mortality, ICU admission rate, length of stay, 30-day and 1-year all-cause readmission rates.

Results: Of the 2,220,000 cases, 51.3% were male with a mean age of 68.0 years (standard deviation 17.4). A total of 1,769,530 (79.7%) were multimorbid with a median of 4 (interquartile range 2–6) chronic conditions. The prevalence of multimorbidity increased by about 1.0% per year over the 6-year study period from 76.1% (2012) to 82.2% (2017). Multimorbidity was associated with higher odds of in-hospital mortality (odds ratio [OR] 1.31, 95% confidence interval [CI] 1.28 to 1.34), ICU admission rate (OR 3.29, 95% CI 3.23 to 3.34), length of stay (+2.7 days, 95% CI 2.6 to 2.7), 30-day- (OR 1.92, 95% CI 1.89 to 1.94) and 1-year all-cause readmission rates (OR 1.70, 95% CI 1.68 to 1.71). The associations with in-hospital mortality and readmission were strongest in younger patients.

Conclusions: Multimorbidity is highly prevalent in medical inpatients and has a relevant association with poor healthcare outcomes. Further investigation is needed to specify risk factors as well as to optimise the management of multimorbid patients to improve outcomes.