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

This study has several limitations. As in similar studies, no potential etiology was identified for a sizeable group of participants. Despite the high level of patient inclusion, we were not able to collect all tests for all participants: a more complete sample set might have resulted in the detection of more potential pathogens. We chose to collect oropharyngeal swabs for PCR analysis to optimize sample collection and patient recruitment. It is possible that use of nasopharyngeal samples may have increased sensitivity for respiratory viruses [40] . In addition, an organism identified from the upper airway cannot always be assumed to be the causative agent for pneumonia, and PCR results for some organisms must be interpreted as suggestive for possible etiology. It is also possible that our method of batch analysis and storage may have decreased the sensitivity of our laboratory methods. When comparing the statistical results of this study, the number of relevant variables in comparison with the cohort size, particularly for individual etiologies, must be kept in mind as in other comparable studies. We applied multinomial regression as part of our analysis, but there is a risk of overfitting due to small numbers of individual outcomes, cohort size, and number of variables. The results of direct comparisons are reported alongside these results but must also be interpreted with the number of comparisons in mind. Both of these factors increase the risk of type I error.