Multiple comorbidities as risk factors for community-acquired pneumonia in elderly frail patients admitted to an acute medical ward: a retrospective study

Background – Pneumonia is one of the most frequent causes of hospital admission for elderly frail patients. These patients often show a high degree of clinical complexity with a large number of comorbidities affecting multiple organs. While some specific diseases are well known in literature for acting as risk factors for pneumonia, such as congestive heart failure, COPD and diabetes, little is known about the role of the overall burden of comorbidity. Aims – Our aim was to investigate the possible role of different chronic comorbidities, both considered singularly and together in a literature-validated complexity index, as risk factors for pneumonia in a cohort of elderly frail patients admitted to hospital. Materials and methods – At Internal Medicine and Critical Subacute Care Unit of Parma University Hospital (94 beds managed by care intensity) we carried out a retrospective evaluation of the clinical records of all patients over 65 years old admitted to the Acute Care Ward from the Emergency Department during a 8-month period (January-August 2013). For each patient we recorded age, origin (community vs nursing home), main diagnosis, type and severity of chronic comorbidities, pneumonia status, length of stay and drug therapy with proton pump inhibitors (PPIs). For each patient we calculated indexes of clinical complexity such as CIRS (Cumulative Index Rating Scale) Comorbidity Score and CIRS Severity Index. Statistical analysis was performed with chi-square test, Mann-Whitney’s U test, odds ratio and binary logistic regression whenever appropriate. Results – 1199 patients (546 M, 653 F, mean age 78 ± 13 years) were evaluated. The most frequent comorbidities were cardiovascular diseases (54%), COPD (30%), cancer (29%) and dementia (27%). 239 patients (20%, 138 M, 101 F) were discharged with a diagnosis of pneumonia. CIRS comorbidity score was significantly higher in patients with (median 14, IQR 10-17) than in patients without pneumonia (median 12, IQR 8-16, p<0.01). The risk for pneumonia was 1.5-fold higher for subjects with a CIRS comorbidity score >8 (OR 1.5, IC95% 1.1-2.1, p<0.05) and 1.6-fold higher for subjects with a CIRS severity index >4 (OR 1.6, IC95% 1.1-2.3, p<0.05). COPD (OR 2.7, IC95% 2.0-3.6, p<0.0001), dementia (OR 2.3, IC95% 1.7-3.1, p<0.0001) and nursing home residency (OR 1.9, IC95% 1.3-2.9, p<0.005) proved to be the strongest single risk factors, also confirmed by a multivariate model of binary logistic regression. Stroke, cancer, diabetes, cardiovascular diseases, chronic renal failure, cirrhosis and long-term therapy with PPIs were unrelated to pneumonia risk. Median length of stay was significantly longer in patients with (4 days, IQR 3-7) than in patients without pneumonia (3 days, IQR 2-5, p<0.0001). Conclusions – In elderly frail patients admitted to hospital acute wards, a high chronic comorbidity burden may be a relevant risk factor for pneumonia. The single most relevant risk factors are COPD, dementia and nursing home residency, while other traditional risk factors like diabetes seem to have little influence in this population.