ABSTRACT
INFECTIONS RELATED TO CHRONIC OBSTRUCTIVE PULMONARY DISEASES Cigarette smoking is the single most important risk factor of both COPO and lung cancer. It impairs mucociliary clearance, which is the primary defense mechanism of the respiratory system. Oamaged respiratory tract epithelium decreases ciliary mucous clearance. Viral infections cause release of inflammatory mediators, increase local permeability, and predispose the airway to bacterial colonization. Haemophilus influenza especially produces substrate to impair ciliary function, increase mucous production, and destroy local immunoglobulin and impair neutrophil fuction. Acute tracheobronchitis preceding acute exacerbations of COPO and community-acquired pneumonia invariably occur in patients with lung cancer. Most COPO exacerbations are caused by bacterial infections or viral tracheobronchitis superinfected by bacterial pathogens. Community-acquired pneumonia in COPO patients is generally caused by Streptococcus pneumoniae, H. influenzae, and Moraxella catarrhalis [2]. Patients present with cough (more than 90%), dyspnea, sputum production, and pleuritic chest pain [3,4]. Sometimes, pneumonia itself is the first presentation oflung cancer, especially unresolving pneumonia despite appropriate treatment. Severe community-acquired pneumonia is increased in patients with underlying COPO and malignancy, with a higher risk of respiratory failure and mortality. The important pathogens are S. pneumoniae, Legionella pneumophila, H. injl.uenzae, Staphylococcus aureus, and less commonly gram-negative enteric pathogens [5]. Bacteremia is a more common presentation when multilobar pneumonia is present. Regardless of the pathogen, bacteremia is not an indicator of disease severity. However, the yield of a blood culture is higher in patients with severe pneumonia, and the result of identifying the pathogen will facilitate appropriate antibiotic selection [5,6]. Patients with severe COPO are also at risk for nontuberculous mycobacterial infections. The common pathogens are Mycobacterium avium complex (MAC), Mycobacterium kansasii; less commonly, M. abscessus, M. chelonae, M. malmonense, and M. xenopi [7]. Presentations of nontuberculous mycobacterial infections resemble tuberculosis with fever, weight loss, hemoptysis, and progressive dyspnea. Radiographic findings are cavitary lesions, pulmonary nodules, bronchiectasis, and infiltrates. MAC infection in patients with COPO and lung cancer rarely disseminates outside the lung [7,8].
