Incidence, Etiology, and Outcomes of Community-Acquired Pneumonia: A Population-Based Study

Bjarnason, Agnar; Westin, Johan; Lindh, Magnus; Andersson, Lars-Magnus; Kristinsson, Karl G; Löve, Arthur; Baldursson, Olafur; Gottfredsson, Magnus

Mortality was relatively low (3%) compared with many previous studies (2%-15%), possibly due to differences in setting and inclusion criteria [3, 4, 7, 12, 39] . Jain et al [12] found a similar mortality (2%) in their cohort and a similar PSI score despite being younger, whereas 21% of their patients were admitted to ICU and 6% required invasive ventilation. Corresponding results from this study are 5% and 2%, respectively, if cases due to the H1N1 pandemic are excluded (Table 5) . Conversely, the median LOS was 3 days in the study by Jain et al [12] compared with 7 in the current study, probably reflecting major differences in management approaches to this problem between a Nordic country and the United States. Holter et al [11] examined a Norwegian cohort with an identical median age to ours and found a similar LOS (7 days), and although 18% were admitted to ICU, the mortality was 4%. It is likely that systemic factors and different thresholds for ICU admission, timing of switching from intravenous to oral, and transfer to outpatient management may explain some of these differences [11, 12] . Rates of ICU admissions, use of assisted ventilation, and LOS were similar for patients irrespective of organisms identified. It is notable that patients with atypical pathogens had lower PSI and CURB-65 scores than other patients but required similar ICU care and LOS. Because both scores include age as risk factors, the relatively low age of influenza and M pneumoniae patients may offer a partial explanation. Severity scores and outcomes were also similar for patients with an identified virus when compared with other patients. Although pandemic influenza cases heavily influenced this result, they did not account for all morbidity in this group. Patients with dual pathogens had a trend towards worse outcomes, but the number of patients was low and therefore a great potential for type II error.