Clinical impact of combined viral and bacterial infection in patients with community-acquired pneumonia

Abstract

Background: New methods for identifying respiratory pathogens have led to several reports of a high yield of mixed infections in patients with community-acquired pneumonia (CAP). The clinical impact of these findings has, however, not been fully evaluated. We aimed to compare patients with a pure bacterial etiology with those with findings of both bacteria and virus regarding severity of illness and length of hospital stay. Methods: Adults with CAP admitted to Karolinska University Hospital were studied prospectively (N = 184). Microbiological methods included cultures from blood, sputum and nasopharyngeal secretions; sputum samples analyzed with quantitative real-time polymerase chain reaction for Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis; nasopharyngeal specimens analyzed with polymerase chain reaction and serology for Mycoplasma pneumoniae, Chlamydophila pneumoniae and viruses common in the respiratory tract; and urine antigen assays for detecting pneumococcal and Legionella pneumophila antigens. The pneumonia severity index (PSI) was used to assess the severity of illness. Results: The likelihood of getting a score corresponding to PSI classes IV or V was higher in patients with findings of both bacteria and virus than in those with a bacterial pathogen alone (odds ratio 4.98, 95% confidence interval 2.09–11.89; p < 0.001). The median length of hospital stay was 7 days among patients with mixed infections and 4 days among those with a bacterial etiology alone (p = 0.018). Conclusions: Patients infected with a virus and a bacterial pathogen more often develop severe CAP and have a longer hospitalization than those with a bacterial etiology alone.

Keywords::

• Pneumonia
• bacterial pneumonia
• viral
• prognosis

Acknowledgements

The authors thank Dr Tobias Allander and laboratory assistant Cecilia Lindau, Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, for contributing data regarding unbiased sequence-based molecular virus screening; Dr Christian Giske, Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, Stockholm, and Dr Carl Spindler, Department of Infectious Diseases, Karolinska University Hospital Solna, Stockholm, for contributing data regarding the sputum RQ-PCR results; medical students Rima Dandachi and Wilhelm Hedin, Karolinska Institutet, Stockholm, for helping with data compilation; respiratory physiotherapists Susanna Wennman and Annette Idengren, Department of Physiotherapy Karolinska University Hospital Solna, Stockholm, for collection of sputum samples; and Elisabeth Berg, Karolinska Institutet LIME/MedStat, for assistance with statistics.

Declaration of interest: The study was supported by grants from Karolinska Institutet and the Swedish Strategic Programme against Antibiotic Resistance. The funding sources had no role in the study design, data collection, data analysis or interpretation, or writing of the report. The authors have no conflicts of interest to disclose.