COPD is one of the most important causes of morbidity and mortality and supposes a sanitary problem in Europe and USA. Patients with COPD usually have 1-2 episodes of acute exacerbation of COPD (AECOPD) per year, being these the principal causes of of hospitalizations, respiratory problems and medical visits. After an episode of AECOPD, the majority of patients develop a transitory (or permanent) worsening in their quality of life and 50% of them will require a new hospitalization. Globally, a 75%& of the exacerbations might be associated with a respiratory tract infection, and among them, 50% might be related to bacteria and in 45% an evidence of viral infection could be documented. Even though the antibiotic treatment might not be useful for a majority of patients with AECOPD, is generalized its use(almost an 85% in some series) in hospitalized patients. The non-controlled use of antibiotics in AECOPD results in a very expensive disease and raises the rate of resistance of bacteria. The available literature have shown that there's a relation between exacerbations and infections, based on sputum samples.