According to international recommendations, severe COPD exacerbations should be treated with antibiotics. However, these recommendations are based on limited evidence, including old studies with small group of patients. Systematic virological testing by RT-PCR suggests that viruses are responsible for more than half of these exacerbations, although the causal link is not yet clearly established. To date, neither clinical nor biological markers can help distinguish an exacerbation caused by a virus from those due to other causes.