What is bacterial colonisation in COPD?

Case history: A 62-year-old male presents with chronic exertional dyspnoea, early morning productive cough and intermittent wheezing. He is a former smoker with a smoking history of 40 pack-years. He states that his symptoms are gradually progressive, he does have “bad days of increased dyspnoea, cough and sputum” quite often, but he does not seek medical care for them as he does not want to bother his doctors. Instead, he increases his inhaled bronchodilators and reduces his activities until these episodes resolve. He has had only one medically treated exacerbation in the past year, when he had to come to the emergency room because his breathing “got really bad”. Spirometry shows severe airflow obstruction without a bronchodilator response. His outpatient medication includes a tiotropium inhaler once daily and a budesonide–formoterol inhaler twice a day. Sputum cultures carried out at this visit show 3+ Nontypeable Haemophilus influenzae (NTHi). What is the significance of his sputum culture results? How did he get colonised with NTHi, is it of clinical significance, and does it need treatment? If yes, how do we treat such colonisation? Chapter summary: It is likely that chronic bacterial presence in COPD airways, usually referred to as colonisation, is in fact a chronic infectious state. Several investigations have now demonstrated that the presence of bacteria in the lower respiratory tract in stable COPD is associated with increased inflammation. Pathological and radiological findings in COPD support chronic infection, as do recent mouse models. Increased daily respiratory symptoms and unreported exacerbations are clinical manifestations of chronic infection in COPD. Chronic infection in this disease results from multiple impairments of innate lung immunity induced by exposure to noxious particles or gases such as tobacco smoke.