Pneumonia and influenza hospitalizations in elderly patients with comorbidities

The presence of comorbidities in the elderly (65+ years old) increases the risk of complications due to influenza. This study explores patterns of comorbidity within patients admitted to the hospital with pneumonia and influenza (P&I), and compares the differences in clinical outcomes with respect to age. All records of hospitalization due to P&I between 1991 and 2004 were abstracted from Centers for Medicare and Medicaid Services (CMS) databases and examined for 30 common comorbidities using the Elixhauser Comorbidity Software. Of the 16,441,462 P&I records, nearly 90% of records had at least one comorbidity (mean number of comorbidities: 2.14, SD: 1.34). The most common comorbidities were chronic pulmonary diseases (37.2%), cardiovascular diseases (28.0%), and diabetes (17.7%). The number of comorbidites and P&I rates increase exponentially with age, exhibiting inflection points at approximately 72, 83, and 95 years. The normalized age-specific curves in patients with cancer, diabetes, and cardio-vascular diseases exhibited a substantially steeper increase compared to the elderly who are free of comorbidities. For example, national rates of influenza at 65, 75, and 85 were 14.8, 27.6, and 67.9 cases per year per 1000 elderly respectively, but the probability of being hospitalized for influenza for a 75-year old patient with cancer is comparable to the probability of being hospitalized for an 85 year old person without comorbidities. These preliminary results suggest that elderly patients with comorbidities have much higher hospitalization rates and are immunologically older compared to patients free of comorbidities at the same chronological age.