Background
To describe the prevalence of multimorbidity and to study the association between acute and chronic diseases in acutely hospitalized older patients

Methods
Prospective cohort study conducted between 2006 and 2008 in three teaching hospitals in the Netherlands. 639 patients aged 65 years and older, hospitalized for > 48 h were included. Two physicians scored diseases, using ICD-9 codes. Chronic multimorbidity was defined as the presence of ≥ 2 chronic diseases, and acute multimorbidity as ≥ 1 acute diseases upon pre-existent chronic diseases. Logistic regression analyses were conducted to analyse cluster associations between a chronic index disease and the concurrent chronic or acute disease, corrected for age and sex.

Results
The mean age of patients was 78 years, over 50% had ADL impairments. Prevalence of chronic multimorbidity was 69%, and acute multimorbidity was present in 88%. Hypertension (OR 1.16; 95% CI 1.08–1.24), diabetes (type I or type 2) (OR 1.12; 95% CI 1.04–1.21), heart failure (OR 1.25; 95% CI 1.14–1.38) and COPD (OR 1.19; 95% CI 1.05–1.34) were associated with acute renal failure. Hypertension (OR 1.10; 95% CI 1.04–1.17) and atrial fibrillation (OR 1.17; 95% CI 1.08–1.27) were associated with an adverse drug event. Gastro-intestinal bleeding was clustered with atrial fibrillation (OR 1.11; 95% CI 1.04–1.19) and gastric ulcer (OR 1.16; 95% CI 1.07–1.25).

Conclusion
Both acute and chronic multimorbidity was frequently present in hospitalized older patients. We identified specific associations between acute and chronic diseases. There is a need for strategies addressing multimorbidity during the exacerbation of chronic diseases.