THE ROLE OF INFECTION IN COPD

Clinical studies of acute exacerbations of COPD are difficult because of the heterogeneous nature of COPD, diffuse symptoms that can vary sp ontaneously, and difficulties in defining clinical response both in th e short and long term. The role of bacterial infection, and thus use o f antibiotics, in COPD is controversial. The available evidence shows that bacterial infection has a significant role in acute exacerbations , but its role in disease progression is less certain. Upper respirato ry tract commensals, such as nontypable Haemophilus influenzae, cause most bronchial infections by exploiting deficiencies in the host defen ses. Some COPD patients are chronically colonized by bacteria between exacerbations, which represents an equilibrium in which the numbers of bacteria are contained by the heat defenses but not eliminated. When an exacerbation occurs, this equilibrium is upset and bacterial number s increase, which incites an inflammatory response. Neutrophil product s can further impair the mucosal defenses, favoring the bacteria, but if the infection is overcome, symptoms resolve. However, if the infect ion persists, chronic inflammation may cause lung damage. About half o f exacerbations involve bacterial infection, but these patients are no t easy to differentiate from those who are uninfected, which means tha t antibiotics have to be given more often than is strictly necessary. Further research is needed to characterize those patients in whom bact erial infection has a more important role.