C-reactive protein level and microbial aetiology in patients hospitalised with acute exacerbation of COPD

Both viruses and bacteria are thought to cause exacerbations of chronic obstructive pulmonary disease (COPD); however, the relative importance of each remains uncertain. C-reactive protein (CRP) levels increase during exacerbations but the relationship with aetiology is not established. We aimed to explore the relationship between serum CRP and the rate of detection of viruses and bacteria. This was a prospectively recruited, observational study of patients hospitalised with exacerbations of COPD. Nasopharyngeal swabs were tested for respiratory viruses by reverse transcriptase-PCR. Sputum and blood were collected for bacterial culture and urine tested for pneumococcal antigen. CRP levels were measured on sera. CRP and other factors associated with viral, bacterial or mixed detection were assessed using multiple logistic regression analysis. 264 patients with exacerbations of COPD were studied: 26% tested positive for respiratory viruses only, 13% had bacteria only, 12% had mixed viral/bacterial detection, and 49% had no pathogens detected. CRP level and temperature were strongly associated with viral detection rate (p<0.001 and p=0.004, respectively) and mixed viral/bacterial detection rate (p=0.02 and p=0.03, respectively) on multivariate analysis. Bacterial detection rate was not associated with CRP level or body temperature. This study supports the role of viruses as important aetiological agents causing exacerbations of COPD.