Background
Respiratory viruses are well-known causes of acute exacerbation of chronic obstructive pulmonary disease (AE-COPD) and also important pathogens for concomitant pneumonia in COPD (CP-COPD). However, distributions and clinical impacts of respiratory viruses between the two groups have not been well investigated.

Methods
Clinical and microbiological data from 477 COPD patients admitted with AE-COPD (n=241) or CP-COPD (n=236) who underwent a multiplex respiratory virus RT-PCR test were retrospectively reviewed between January 2010 to December 2012. Demographic characteristics, identified viruses, and clinical features and outcomes were compared between the two groups.

Results
The baseline mean FEV1 was lower in the AE-COPD group than in the CP-COPD group. Respiratory viruses were identified in 41.9% of AE-COPD group and 33.5% of the CP-COPD groups. The most common virus was influenza virus in the AE-COPD group (33.7%) vs. human coronavirus (24.1%) in the CP-COPD group. Only influenza viral infection rate was significantly higher in AE-COPD group than CP-COPD group. Among patients who had viral infection, bacterial co-infection was common both in AE-COPD (41.6%) and CP-COPD group (50.6%). In-hospital mortality of AE-COPD and CP-COPD were 1.2% and 12.3%, respectively (P < 0.01). Among CP-COPD patients, mortalities of patients with sole viral infection, sole bacterial infection, and viral-bacterial co-infection were 2.6%, 25.8%, and 16.9%, respectively (P = 0.01).

Conclusions
Respiratory viruses were commonly identified in both AE-COPD and CP-COPD, the distribution of identified viruses between two groups showed different patterns. The mortality rates of sole viral infection group was significantly lower than sole bacterial or viral-bacterial co-infection group in CP-COPD patients.