Hospitalization Due to Infections Before and After Alzheimer's Disease Diagnosis.

Objectives: There is a lack of studies on the rate and temporal changes of infections in relation to Alzheimer's disease (AD) diagnosis. We studied the infection rate in persons with and without AD yearly 5 years before and after AD diagnosis.

Design: Register-based cohort study.

Setting and participants: We used the Medication Use and Alzheimer's Disease cohort with 70,718 Finnish community dwellers diagnosed with AD between 2005 and 2011 and an equal number of age, sex- and region-of-residence-matched comparison persons.

Methods: Data on comorbidities, medication use, and hospital days due to infection were retrieved from multiple nationwide registers. The rate of hospitalization and accrued hospital days due to infections were calculated yearly during the follow-up. The accumulation of hospital days was investigated with the negative binomial model.

Results: During the follow-up, one-half of persons with AD had inpatient stays due to infections compared with 34% of persons without AD. The infection rate increased substantially 1 to 2 years before AD diagnosis. At AD diagnosis, the rate of inpatient stays and outpatient visits due to infection was higher (15 per 100 person-years) in persons with AD than in comparison persons (9 per 100 person-years), and the accumulation of hospital days in persons with AD was higher a year after the diagnosis (incidence rate ratio, 1.21; 95% CI, 1.11-1.32) due to higher infection rate. The most common infection diagnoses in both groups were pneumonia and genitourinary infections.

Conclusions and implications: Compared with matched comparison persons, the higher hospitalization rate due to infections could be caused by systemic inflammation related to AD, infections generally treated in outpatient care, delirium symptoms associated with infections, and caregiver burden. The prevention of infections should be part of the care of cognitive disorders throughout the disease.